Improved microwave synthesis of unsymmetrical N,N'-diaryl-1,2-aminoethane and imidazolidinium salts as precursors of N-heterocyclic carbenes

Abstract

Lithium aluminium hydride reduction of bis-unsymmetric-diaryloxamides 3 is difficult to accomplish especially for the sterically hindered mesityl derivative. Using microwaves LAH reduction of 3a,d was successful in a short time, however, with cleavage of the ether linkage to give compounds 11a,d. Extension of this method enabled the reduction of bis-oxamide derivatives 13 to the corresponding tetraamine derivative 14 which was then converted to the bis-imidazolidinium salt 15. Application of this method led to rapid reduction of unsymmetric N,N'-diaryloxamides 16 to the corresponding N,N'-diarylethylenediamines 17 which were converted to their corresponding imidazolidinium salts 18.

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Introduction

Since their discovery, N-heterocyclic carbenes (NHCs) have attracted considerable attention due to their extensive applications as organocatalysts, ligands in organometallic chemistry and in transition metal catalysis.^1–3 Increasing interests in the synthesis and applications of N-heterocyclic carbenes derived from imidazolium ions and related heterocyclic derivatives have been the subject of many recent papers and reviews.^1–10 Of important significance is their use as an alternative ligands to phosphines in the design of new organometallic catalysts of attractive important applications in metathesis and coupling reactions. The remarkable stability of transition metal complexes of NHC compared to their phosphine counterparts contributed considerably to the recent advances in the developments of these ligands and the design of new organometallic catalysts with wider application in organic chemistry. NHC act as excellent ligands forming complexes with palladium, ruthenium, nickel, rhodium, iridium, gold, copper and silver yielding useful organometallic catalysts. These organometallic catalysts were efficiently used in many catalytic reactions including olefin metathesis, transfer hydrogenation, Heck, Suzuki and Sonogashira coupling reactions, as well as many other homogeneous catalytic reactions.^1,7–10

In this work we report our attempts to synthesize bis-imidazolidinium salts 1 to study their possible catalytic application as well as their potentialities in preparing bis-NHC for possible ligation with different metals. Scheme 1 illustrate the proposed reterosynthetic strategy for the synthesis of 1.

Scheme 1

Results and discussion

Scheme 2 illustrates the synthesis of the starting bis-oxamide derivatives 3. Three different routes have been used for the synthesis of compounds 3 utilizing bis-alkylation of phenolic compounds (routes A) and traditional amidation methods (route B and C).

Scheme 2 Synthetic approaches of the tetra-amides 3a–g.

Reduction of the tetraamides 3 has now been investigated in an attempt to synthesize the corresponding tetraamines 2 which are the precursors of target imidazolinium salts 1. Scheme 3 illustrates the products 2, 9, 10, 11 obtained by lithium aluminum hydride reduction of bis-oxamide derivatives 3. Thus, LAH reduction of 3a in dry ether afforded the corresponding tetramine 2a; which crystallized out from the ethereal solution; together with 1,2-dianilinoethane 9a as minor by-product. Similar LAH reduction of 3b,c yielded 2b,c. On the other hand, LAH reduction of compound 3d in refluxing ether gave only the bis-amide 10d after 24 h. The high insolubility of the other bis-oxamides 3e–g in refluxing ether or even THF led upon LAH reduction to the formation of complex mixture containing mainly unreacted starting materials.

Scheme 3

The conversion of 2a,b into the target bis-imidazolinium salts 1a,b has been readily achieved upon heating the hydrochloride salt 2a with triethyl orthoformate at 110 °C for 24 h or by heating 2a,b under reflux for 24 h in toluene with ammonium tetrafluoroborate and triethyl orthoformate with catalytic amount of formic acid.

To overcome the difficulties in the LAH reduction of compounds 3c–g we investigated the use of microwave reactors for achieving this reduction at higher temperature. Thus, heating each of 3a,d with LAH in ether at 110 °C in microwave gave compounds 11a,d. Although under this conditions all amide groups were successfully reduced to the corresponding amines, the compounds have also been reduced at the ether linkage. This method appears to be a short good method for sterically hindered oxamide derivatives. We therefore investigated the application of this microwaves LAH reduction procedure for the synthesis of many important imidazolium salts.

Scheme 4 illustrate the successful synthesis of the bis-imidazolium 15 starting with bis(4-aminophenyl)methane12 using microwaves LAH reduction as the key step for obtaining the tetraamine 14.

Scheme 4 Synthesis of bis-imidazolidinium salt 15. Ar = 2,4,6-(CH₃)₃C₆H₂.

The same method has also been applied for the synthesis of many other simple imidazolinium salts 18a–c (Scheme 5). The microwaves LAH reduction of asymmetric oxamides 16 give reasonable yield of the corresponding substituted 1,2-diaminoethane 17a–c in short time compared to other reported conditions which requires very long refluxing time in high boiling solvent (DME).¹² Compounds 17a–c were readily converted to the corresponding imidazolinium salts 18a–c.

Scheme 5

Conclusion

In this work during our attempt to prepare bis-imidazolidinium salts we discovered an improved rapid application of microwaves in lithium aluminum hydride reduction of sterically hindered unsymmetric N,N'-diaryloxamides to the corresponding N,N'-diarylethylenediamines. This provides an expedient method to synthesize the stericaly hindered N,N'-diaryl-1,2-diaminoethane thus facilitates the synthesis of many important imidazolidinium and bis-imidazolidinium salts which have many important applications specially as precursors of N-heterocyclic carbenes.

Experimental

General

All melting points are uncorrected. The microwave oven used was a single mode cavity explorer microwave (CEM Corporation, NC, USA) and irradiation was conducted in heavy-walled pyrex tubes (capacity 10 mL). IR spectra were recorded in KBr disks on a Perkin Elmer System 2000 FT-IR spectrophotometer. ¹H and ¹³C NMR spectra were recorded on a Bruker DPX 400, 400 MHz, Avance^II 600, 600 MHz super-conducting NMR spectrometers. Mass spectra were measured on GCMSDFS-Thermo and with LCMS using Agilent 1100 series LC/MSD with an API-ES/APCI ionization mode. Microanalyses were performed on LECO CH NS-932 Elemental Analyzer.

Synthesis of oxalamic acid ethyl ester: general procedure

To an ice cold (0–5 °C) stirred solution of substituted aniline (10 mmol) or compound 7 (5 mmol), and triethylamine (1 mL, 10 mmol) in DCM (30 mL) was added ethyl chlorooxoacetate (1.1 mL, 10 mmol) in DCM (10 mL). The reaction mixture was stirred for 1 h in ice and stirring was continued overnight at room temperature. The solvent was then removed in vacuo and the remaining precipitate was washed with water. The solid obtained was crystallized from ethanol to give the corresponding oxalamic esters 4a–d and 8a.

N-Phenyloxalamic acid ethyl ester 4a. Colorless crystals; yield 0.16 g (83%); mp 66 °C (lit.¹³ mp 64–66 °C); δ_H(400 MHz, CDCl₃) 1.44 (t, 3H, J 7.2), 4.43 (q, 2H, J 7.2), 7.20 (t, 1H, J 7.6), 7.39 (t, 2H, J 8.0), 7.66 (d, 2H, J 8.0), 8.96 (s, 1H); δ_C(CDCl3, 100 MHz) 14.2, 64.0, 120.0, 125.7, 129.4, 136.5, 154.1, 161.2.

N-4-Methoxyphenyloxalamic acid ethyl ester 4b. Colorless crystals; yield 0.19 g (85%); mp 100 °C (lit.¹⁷ mp 100–104 °C); δ_H(400 MHz, CDCl₃) 1.42 (t, 3H, J 7.2), 3.80 (s, 3H), 4.41 (q, 2H, J 7.2), 6.90 (d, 2H, J 8.8), 7.56 (d, 2H, J 8.8), 8.80 (s, 1H); δ_C(CDCl3, 100 MHz) 14.2, 55.6, 63.8, 114.5, 121.6, 129.7, 153.9, 157.3, 161.3.

N-4-Tolyloxalamic acid ethyl ester 4c. Colorless crystals; yield 0.16 g (80%); mp 65–67 °C (lit.¹⁷ mp 65–67 °C); δ_H(400 MHz, CDCl₃) 1.42 (t, 3H, J 7.2), 2.33 (s, 3H), 4.40 (q, 2H, J 7.2), 7.17 (d, 2H, J 8.4), 7.52 (d, 2H, J 8.4), 8.83 (s, 1H); δ_C(CDCl3, 100 MHz) 14.1, 21.1, 63.8, 120.0, 129.9, 134.0, 135.5, 154.0, 161.3.

N-(2,4,6-Trimethylphenyl)oxalamic acid ethyl ester 4d. Colorless crystals; yield 0.14 g (90%); mp 77–78 °C (lit.¹⁴ mp 76–78 °C); δ_H(400 MHz, CDCl₃) 1.44 (t, 3H, J 7.2), 2.20 (s, 6H), 2.28 (s, 3H), 4.43 (q, 2H, J 7.2), 6.92 (s, 2H), 8.35 (s, 1H); δ_C(CDCl3, 100 MHz) 14.2, 18.5, 21.1, 63.8, 129.3, 129.6, 134.9, 137.9, 155.0, 161.2.

N-(2-{3-[2-(Ethoxyoxalylamino)-phenoxy]-propoxy}-phenyl)oxalamic acid ethyl ester 8a. Colorless crystals; yield 0.36 g (80%); mp 106 °C; ν_max(KBr)/cm⁻¹ 3385, 3370, 2990, 2970, 2927, 2890, 1702, 1602, 1541, 1489, 1455, 1413, 1368, 1336, 1291, 1250, 1208, 1176, 1113, 1044, 1028, 1012, 748; 668; δ_H(400 MHz, CDCl₃) 1.42 (t, 6H, J 7.2), 2.45 (quint, 2H, J 6.0), 4.32–4.42 (m, 8H), 6.97–7.03 (m, 4H), 7.12 (dt, 2H, J 8.0, 1.2), 8.39 (dd, 2H, J 8.0, 1.2), 9.56 (s, 2H); δ_C(CDCl₃, 100 MHz) 14.2, 29.4, 63.8, 65.2, 111.5, 120.1, 121.7, 125.5, 126.5, 147.7, 153.7, 161.2; m/z (EI) 455 (M⁺); m/z (EI) 458.1683 (M⁺, C₂₃H₂₆N₂O₈ requires 458.1683).

Synthesis of oxamides 5a–d: general procedure

A mixture of each of compounds 4a–d (1 mmol), o-aminophenol (0.109 g, 1 mmol) and boric acid (0.005 g) was heated at 170 °C for 1 h. The solid obtained was boiled in ethanol and the insoluble solid was collected to give products 5a–d.

N-2-Hydroxyphenyl-N′-phenyloxalamide 5a. Brown powder; yield 0.19 g (75%); mp 263–264 °C (lit.¹⁵ mp 261–262 °C); δ_H(400 MHz, DMSO) 6.89 (t, 1H, J 7.6), 6.95 (d, 1H, J 7.6), 7.02–7.04 (m, 1H), 7.18 (t, 1H, J 7.6), 7.39 (t, 2H, J 8.0), 7.87 (d, 2H, J 8.0), 8.16 (d, 1H, J 8.0), 8.12 (d, 1H, J 8.0), 9.88 (s, 1H), 9.89 (s, 1H) 10.41 (s, 1H), 10.42 (s, 1H), 10.86 (s, 1H), 10.95 (s, 1H); δ_C(DMSO, 100 MHz) 115.0, 115.1, 119.3, 119.7, 119.9, 120.5, 120.7, 124.65, 124.72, 124.8, 125.0, 125.3, 125.5, 128.8, 137.5, 137.7, 147.1, 147.3, 157.1, 157.2, 158.4, 158.6; m/z (EI) 256 (M⁺); m/z (EI) 256.0842 (M⁺, C₁₄H₁₂N₂O₃ requires 256.0842).

N-2-Hydroxyphenyl-N′-4-methoxyphenyloxalamide 5b. Colorless powder; yield 0.23 g (80%); mp 216–217 °C; δ_H(400 MHz, DMSO) 3.75 (s, 3H), 6.88 (dt, 1H, J 6.8, 1.2), 6.95 (d, 2H, J 8.8), 7.03 (dt, 1H, J 7.2, 1.6), 7.77–7.80 (m, 2H), 8.17 (dd, 2H, J 8.0, 1.6), 9.89 (s, 1H), 10.41 (s, 1H), 10.86 (s, 1H); δ_C(DMSO, 100 MHz) 20.5, 115.1, 115.1, 119.3, 119.6, 119.9, 120.4, 120.5, 124.7, 125.0, 125.2, 125.6, 129.1, 133.7, 133.9, 134.9, 135.2, 147.1, 147.3, 157.1, 157.2, 158.1, 158.5; m/z (EI) 286 (M⁺); m/z (EI) 286.0948 (M⁺, C₁₅H₁₄N₂O₄ requires 286.0948).

N-2-Hydroxyphenyl-N′-4-tolyloxalamide 5c. Brown powder; yield 0.14 g (52%); mp 228–229 °C (lit.¹⁵ mp 221–222 °C); ν_max(KBr)/cm⁻¹ 3339, 3243, 3220, 3126, 3036, 1658, 1610, 1593, 1534, 1458, 1375, 1283, 1228, 1195, 1100, 814, 745; δ_H(400 MHz, DMSO) 2.28 (s, 3H), 6.88 (dt, 1H, J 6.8, 1.2), 6.95 (d, 2H, J 8.8), 7.03 (dt, 1H, J 7.2, 1.6), 7.77–7.80 (m, 2H), 8.17 (dd, 2H, J 8.0, 1.6), 9.90 (s, 1H) 10.42 (s, 1H), 10.88 (s, 1H); δ_C(DMSO, 100 MHz) 20.5, 115.0, 115.1, 119.3, 119.6, 119.9, 120.4, 120.5, 124.7, 125.0, 125.2, 125.6, 129.1, 133.7, 133.9, 134.9, 135.2, 147.1, 147.3, 157.1, 157.2, 158.1, 158.5; m/z (EI) 270 (M⁺); m/z (EI) 270.0999 (M⁺, C₁₅H₁₄N₂O₃ requires 270.0999).

N-2-Hydroxyphenyl-N′-mesityloxalamide 5d. Colorless crystals; yield 0.2 g (70%); mp 196 °C (lit.¹⁴ mp 196 °C); ν_max(KBr)/cm⁻¹ 3371, 3262, 2953, 2921, 2860, 1668, 1601, 1518, 1457, 1358, 1283, 1225, 1102, 1039, 853, 752, 736, 710; δ_H(400 MHz, DMSO) 2.12 (s, 6H), 2.25 (s, 3H), 6.89 (dt, 1H, J 1.2, 8.0), 6.92 (s, 2H), 6.96 (dd, 1H, J 8.0, 1.6), 7.03 (dt, 1H, J 1.6, 8.0), 8.21 (dd, 1H, J 8.0, 1.6), 9.84 (s, 1H), 10.41 (s, 1H), 10.45 (s, 1H); δ_C(DMSO, 100 MHz) 18.0, 20.5, 115.0, 119.4, 125.0, 128.4, 131.4, 134.8, 136.2, 146.9, 157.1, 158.7. m/z (EI) 298 (M⁺); m/z (EI) 298.1312 (M⁺, C₁₇H₁₈N₂O₃ requires 298.1312).

Synthesis of oxalamic acids: general procedures

To a solution of NaOH (0.12 g, 3.0 mmol) in EtOH was added each of 4a,d and 8a (1 mmol). The mixture was stirred overnight. The solvent was then removed in vacuo and the remaining mixture was acidified with drops of dilute HCl. The solid obtained was filtered to give the oxalamic acid.

Phenyloxalamic acid. Colorless crystals; yield 0.12 g (70%); mp 149–150 °C; ν_max(KBr)/cm⁻¹ 3445, 3408, 3303, 1767, 1686, 1602, 1547, 1497, 1448, 1352, 1312, 1244, 1214, 1181, 1167, 1028, 938, 897, 754, 740, 721, 687; δ_H(400 MHz, CDCl₃) 7.12 (t, 1H, J 7.2), 7.34 (t, 2H, J 8.0), 7.76 (d, 2H, J 8.0), 8.17 (br, 1H), 10.67 (s, 1H); δ_C(CDCl3, 100 MHz) 120.1, 126.6, 129.7, 135.6, 155.1, 160.2; m/z (EI) 165 (M⁺); m/z (EI) 165.0421 (M⁺, C₈H₇NO₃ requires 165.0420).

Mesityloxalamic acid. Colorless crystals; yield 0.19 g (90%); mp 106 °C; ν_max(KBr)/cm⁻¹ 3527, 3395, 3364, 3316, 3275, 1713, 1657, 1606, 1531, 1484, 1377, 1313, 1234, 847, 736, 707; δ_H(400 MHz, CDCl₃) 1.42 (t, 6H, J 7.2), 2.45 (quint, 2H, J 6.0), 4.32–4.42 (m, 8H), 6.97–7.03 (m, 4H), 2.18 (s, 6H), 2.29 (s, 3H), 6.92 (s, 2H), 8.51 (s, 1H); δ_C(CDCl3, 100 MHz) 18.3, 20.9, 129.1, 129.2, 134.5, 138.1, 156.8, 160.8; m/z (EI) 207 (M⁺); m/z (EI) 207.0888 (M⁺, C₁₁H₁₃NO₃ requires 207.0889).

N-(2-{3-[2-(Oxalylamino)phenoxy]-propoxy}-phenyl)-oxalamic acid 8b. Colorless crystals; yield 0.39 g (96%); mp 214 °C; ν_max(KBr)/cm⁻¹ 3375, 3358, 3294, 3275, 2970, 2928, 2895, 1761, 1686, 1604, 1543, 1498, 1459, 1346, 1316, 1292, 1264, 1224, 1212, 1118, 991, 781, 751, 690; δ_H(400 MHz, DMSO) 2.28 (quint, 2H, J 6.0), 4.31 (t, 4H, J 6.4), 7.00–6.96 (m, 2H), 7.14 (m, 4H), 8.06 (d, 2H, J 7.6), 9.73 (s, 2H), 14.39 (s, 2H); δ_C(CDCl₃, 100 MHz) 28.5, 65.1, 112.2, 120.3, 120.7, 125.5, 126.0, 148.3, 155.6, 161.9; m/z (EI) 402 (M⁺); m/z (EI) 402.1054 (M⁺, C₁₉H₁₈N₂O₈ requires 402.1058).

Synthesis of arylamino-oxoacetyl chloride: general procedures

A mixture of the appropriate oxalamic acid (1 mmol), thionyl chloride (2 mL) and one drop DMF was heated at 80 °C for 40 min. The excess thionyl chloride was evaporated to give the corresponding acid chlorides 6a,d and 8c.

Anilino-oxoacetyl chloride 6a. Colorless solid; yield 0.07 g (40%); mp 156–157 °C; ν_max(KBr)/cm⁻¹ 3303, 3145, 3092, 3068, 3049, 1767, 1685, 1602, 1548, 1497, 1450, 1352, 1326, 1312, 1247, 1212, 1166, 938, 753, 734, 700; m/z (EI) 183 (M⁺); m/z (EI) 183.0082 (M⁺, C₈H₆ClNO₂ requires 183.0082).

Mesitylamino-oxoacetyl chloride 6d. Colorless solid; yield 0.1 g (45%); mp 175–176 °C; ν_max(KBr)/cm⁻¹ 3323, 3197, 2979, 2960, 2921, 2861, 1770, 1696, 1528, 1483, 1444, 1378, 1342, 1305, 1235, 1208, 1178, 1037, 945, 921, 854, 842, 803, 726, 704, 662; m/z (EI) 225 (M⁺); m/z (EI) 225.0552 (M⁺, C₁₁H₁₂ClNO₂ requires 225.0551).

2-{3-[2-(Chlorooxalylamino)-phenoxy]propoxyphenylamino}-oxoacetyl chloride 8c. Colorless powder; yield 0.4 g (90%); mp 272 °C; ν_max(KBr)/cm⁻¹ 3346, 3296, 1776, 1710, 1691, 1601, 1535, 1492, 1457, 1291, 1257, 1222, 1207, 1120, 994, 981, 750, 651; δ_H(400 MHz, CDCl₃) 2.45 (quint, 2H, J 6.0), 4.33 (t, 4H, J 6.0), 6.98 (dd, 2H, J 8.0, 1.2), 7.04 (dt, 2H, J 1.2, 7.8), 7.18 (dt, 2H, J 1.6, 8.0), 8.33 (dd, 2H, J 8.0, 1.6), 9.15 (s, 2H); δ_C(CDCl₃, 100 MHz) 29.2, 65.2, 111.5, 120.3, 121.8, 125.6, 126.5, 147.8, 151.1, 169.3; m/z (EI) 438 (M⁺); m/z (EI) 438.0378 (M⁺, C₁₉H₁₆Cl₂N₂O₆ requires 438.0379).

Synthesis of oxamides 3a–g: general procedures

Method A. To a solution of KOH (0.3 g, 5.4 mmol) in MeOH (15 mL) was added each of compounds 5a–d (0.15 g, 5.9 mmol). The mixture was stirred at room temperature for 10 min and the solvent was then removed in vacuo. To the mixture was added DMF (1 mL) and the appropriate dibromo derivatives (2.8 mmol). The reaction mixture was heated at 120 °C for 2 h. After cooling, water (20 mL) was added and the solid obtained was collected, boiled with ethanol and the insoluble solid was collected washed with cold ethanol and dried to give the corresponding oxamides 3a–g.

Method B. To a solution of NaOH (0.12 g, 3.0 mmol) in ethanol was added each of compounds 4a,d (1.2 mmol) or 8a (0.6 mmol). The mixture was stirred overnight. The ethanol was evaporated and the mixture was acidified with drops of dilute HCl. The solid obtained was collected and dried to give the corresponding oxalamic acid or bis-oxalamic acid 8b. A mixture of the latter acid (1.2 mmol), thionyl chloride (2 mL) and one drop DMF was heated at 80 °C for 40 min. The excess thionyl chloride was evaporated to give the corresponding acid chloride 6a,d or 8c. To an ice cold (0–5 °C) stirred solution of 7 (0.5 mmol) or the appropriate aromatic amine (1 mmol), and triethylamine (4 mmol) in DCM (30 mL) was added the appropriate acid chloride 6a,d (1 mmol) or 8c (0.5 mmol) in DCM (10 mL). The reaction mixture was stirred overnight at room temperature. The solvent was removed in vacuo and remaining precipitate was washed with water and recrystallized from ethanol to give the corresponding product 3a,d.

Oxo-(2,4,6-trimethylphenylamino)acetyl chloride 6d. Colorless solid; yield 0.1 g (45%); mp 175–176 °C; ν_max(KBr)/cm⁻¹ 3323, 3197, 2979, 2960, 2921, 2861, 1770, 1696, 1528, 1483, 1444, 1378, 1342, 1305, 1235, 1208, 1178, 1037, 945, 921, 854, 842, 803, 726, 704, 662; δ_H(400 MHz, DMSO-d₆) 2.09 (s, 6H), 2.23 (s, 3H), 6.90 (s, 2H), 10.12 (s, 1H); δ_C(DMSO-d₆, 100 MHz) 17.8, 20.5, 128.3, 131.3, 134.7, 136.1, 157.2, 162.2; m/z (EI) 225 (M⁺); m/z (EI) 225.0552 (M⁺, C₁₁H₁₂ClNO₂ requires 225.0551).

N-(2-{3-[2-(Oxalylamino)phenoxy]-propoxy}-phenyl)-oxalamic acid 8b. Colorless crystals; yield 0.39 g (96%); mp 214 °C; ν_max(KBr)/cm⁻¹ 3375, 3358, 3294, 3275, 2970, 2928, 2895, 1761, 1686, 1604, 1543, 1498, 1459, 1346, 1316, 1292, 1264, 1224, 1212, 1118, 991, 781, 751, 690; δ_H(400 MHz, DMSO-d₆) 2.28 (quint, 2H, J 6.0), 4.31 (t, 4H, J 6.4), 7.00–6.96 (m, 2H), 7.14 (m, 4H), 8.06 (d, 2H, J 7.6), 9.73 (s, 2H), 14.39 (s, 2H); δ_C(CDCl₃, 100 MHz) 28.5, 65.1, 112.2, 120.3, 120.7, 125.5, 126.0, 148.3, 155.6, 161.9; m/z (EI) 402 (M⁺); m/z (EI) 402.1054 (M⁺, C₁₉H₁₈N₂O₈ requires 402.1058).

2-{3-[2-(Chlorooxalylamino)-phenoxy]propoxyphenylamino}-oxoacetyl chloride 8c. Colorless powder; yield 0.4 g (90%); mp 272 °C; ν_max(KBr)/cm⁻¹ 3346, 3296, 1776, 1710, 1691, 1601, 1535, 1492, 1457, 1291, 1257, 1222, 1207, 1120, 994, 981, 750, 651; δ_H(400 MHz, CDCl₃) 2.45 (quint, 2H, J 6.0), 4.33 (t, 4H, J 6.0), 6.98 (dd, 2H, J 8.0, 1.2), 7.04 (dt, 2H, J 1.2, 7.8), 7.18 (dt, 2H, J 1.6, 8.0), 8.33 (dd, 2H, J 8.0, 1.6), 9.15 (s, 2H); δ_C(CDCl₃, 100 MHz) 29.2, 65.2, 111.5, 120.3, 121.8, 125.6, 126.5, 147.8, 151.1, 169.3; m/z (EI) 438 (M⁺); m/z (EI) 438.0378 (M⁺, C₁₉H₁₆Cl₂N₂O₆ requires 438.0379).

N-Phenyl-N′-{2-[3-o-(phenylaminooxalylaminophenoxy)propoxy]phenyl}oxamide 3a. Colorless crystals; yield 0.22 g (40%, Method A), 0.36 g (67%, Method B), 0.32 g (59%, Method C); mp 202 °C; ν_max(KBr)/cm⁻¹ 3317, 3288, 3058, 2952, 2931, 1666, 1597, 1520, 1487, 1457, 1442, 1421, 1398, 1321, 1290, 1258, 992, 745, 727, 689; δ_H(400 MHz, CDCl₃) 2.49 (quint, 2H, J 6.0), 4.40 (t, 4H, J 6.0), 7.14–6.98 (m, 6H), 7.21 (tt, 2H, J 7.2, 0.8), 7.41 (t, 4H, J 8.4), 7.67 (dd, 4H, J 8.8, 1.2), 8.36 (dd, 2H, J 8.0, 1.6), 9.32 (s, 2H, NH), 10.01 (s, 2H, NH); δ_C(CDCl₃, 100 MHz) 29.4, 65.3, 112.0, 119.9, 120.0, 121.6, 125.65, 125.67, 126.3, 129.5, 136.5, 148.2, 157.4, 157.8; m/z (EI) 552 (M⁺); m/z (EI) 552.2003 (M⁺, C₃₁H₂₈N₄O₆ requires 552.2003).

N-p-Methoxyphenyl-N′-{2-[3-o-(p-methoxyphenylaminooxalylaminophenoxy)propoxy]-phenyl}oxamide 3b. Colorless crystals; yield 0.27 g (45%); mp 219–221 °C; δ_H(400 MHz, DMSO-d₆) 2.33 (quint, 2H, J 6.0), 3.74 (s, 6H), 4.37 (t, 4H, J 6.0), 6.94 (dd, 3H, J 9.2, 2.8), 7.01 (t, 2H, J 7.6), 7.12 (dd, 2H, J 8.0, 1.2), 7.20 (d, 2H, J 7.6), 7.75 (d, 3H, J 9.2), 8.19 (dd, 2H, J 7.6, 1.2), 10.00 (s, 2H), 10.68 (s, 2H), 10.82 (s, 2H); δ_C(CDCl₃, 100 MHz) 28.6, 55.2, 65.3, 112.4, 119.4, 120.9, 121.9, 122.1, 125.3, 126.1, 130.5, 130.8, 149.0, 157.4, 158.3; m/z (EI) 612 (M⁺); m/z (EI) 612.2213 (M⁺, C₃₃H₃₂N₄O₈ requires 612.2214).

N-p-Methylphenyl-N′-{2-[3-o-(p-methylphenylaminooxalylaminophenoxy)propoxy]-phenyl}oxamide 3c. Colorless crystals; yield 0.17 g (30%); mp 231–232 °C; ν_max(KBr)/cm⁻¹ 3341, 3316, 2954, 2939, 2918, 2888, 1678, 1604, 1595, 1525, 1487, 1452, 1407, 1292, 1257, 1239, 1207, 1113, 1060, 1045, 995, 979, 872, 820, 744, 722; δ_H(400 MHz, DMSO-d₆) 2.29 (s, 6H), 2.35 (quint, 2H, J 6.0), 4.39 (t, 4H, J 6.4), 7.02 (dt, 2H, J 0.8, 8.0), 7.13 (dt, 2H, J 1.6, 8.0), 7.18 (d, 4H, J 8.0), 7.22 (dt, 2H, J 1.2, 8.0), 7.75 (d, 4H, J 8.4), 8.20 (dd, 2H, J 8.0, 1.6), 10.01 (s, 2H, NH), 10.88 (s, 2H, NH); δ_C(DMSO-d₆, 100 MHz) 20.6, 28.7, 65.3, 112.5, 119.5, 120.6, 121.0, 125.4, 126.1, 129.2, 134.0, 135.0, 148.1, 157.3, 158.1; m/z (EI) 580 (M⁺); m/z (EI) 580.2315 (M⁺, C₃₃H₃₂N₄O₆ requires 580.2316).

N-Mesityl-N′-{2-[3-o-(mesitylaminooxalylaminophenoxy)propoxy]-phenyl}oxamide 3d. Colorless crystals; yield 0.38 g (60%, Method A), 0.27 g (42%, Method B), 0.22 g (35%, Method C); mp 220 °C; ν_max(KBr)/cm⁻¹ 3357, 3290, 2953, 2922, 2885, 2859, 1677, 1600, 1539, 1510, 1485, 1453, 1330, 1289, 1254, 1113, 1043, 789, 748, 731, 712; δ_H(400 MHz, CDCl₃) 2.21 (s, 12H), 2.30 (s, 6H), 2.39 (quint, 2H, J 6.0), 4.32 (t, 4H, J 6.0), 6.94 (s, 4H), 6.96–7.09 (m, 6H), 8.36 (d, 2H, J 8.0), 8.78 (s, 2H, NH), 10.00 (s, 2H, NH); δ_C(CDCl₃, 100 MHz) 18.5, 21.1, 29.4, 64.7, 111.7, 119.7, 121.4, 125.5, 126.3, 129.3, 129.9, 135.0, 137.9, 148.1, 157.3, 158.7; m/z (EI) 636 (M⁺); m/z (EI) 636.2942 (M⁺, C₃₇H₄₀N₄O₆ requires 636.2942).

N-Phenyl-N′-[o-(o-phenylaminooxalylaminophenoxymethyl)benzyloxyphenyl]-oxamide 3e. Buff powder; yield 0.43 g (70%); mp 274–275 °C; ν_max(KBr)/cm⁻¹ 3362, 3063, 3034, 2920, 1687, 1600, 1526, 1481, 1445, 1383, 1330, 1295, 1251, 1204, 1113, 1041, 1013, 751, 710, 692; δ_H(400 MHz, DMSO-d₆) 5.47 (s, 4H), 7.01 (t, 2H, J 7.6), 7.10 (dt, 2H, J 8.0, 1.2), 7.16 (t, 2H, J 7.6), 7.28 (d, 2H, J 8.0), 7.37 (t, 4H, J 8.0), 7.44–7.46 (m, 2H), 7.66–7.68 (m, 2H), 7.83 (t, 4H, J 8.0), 8.18 (dd, 2H, J 8.0, 1.6), 10.01 (s, 2H), 10.92 (s, 2H); δ_C(DMSO-d₆, 100 MHz) 67.8, 112.7, 119.8, 120.7, 121.0, 124.8, 125.3, 126.0, 128.4, 128.66, 128.7, 134.7, 137.4, 147.9, 157.3, 158.2; m/z (EI) 614 (M⁺); m/z (EI) 614.2160 (M⁺, C₃₆H₃₀N₄O₆ requires 614.2160).

N-p-Methoxyphenyl-N′-{o-[o-(p-methoxyphenylamino)oxalylaminophenoxymethyl]-benzyloxyphenyl}-oxamide 3f. Buff precipitate; yield 0.44 g (65%); mp 220–221 °C; ν_max(KBr)/cm⁻¹ 3358, 3295, 2932, 2835, 1684, 1599, 1525, 1481, 1454, 1415, 1249, 1205, 1159, 1111, 1033, 827, 750; δ_H(400 MHz, CDCl₃) 3.81 (s, 6H), 5.35 (s, 4H), 6.90–7.00 (m, 6H), 7.03–7.07 (m, 4H), 7.42–7.44 (m, 2H), 7.56–7.61 (m, 6H), 8.35 (dd, 2H, J 6.0, 1.2), 9.19 (s, 2H), 9.93 (s, 2H); δ_C(CDCl₃, 100 MHz) 55.7, 69.1, 112.2, 114.5, 120.1, 121.47, 121.54, 121.7, 125.6, 126.4, 129.2, 129.4, 129.7, 134.5, 147.9, 157.2, 157.6; m/z (EI) 674 (M⁺); m/z (EI) 674.2371 (M⁺, C₃₈H₃₄N₄O₈ requires 674.2371).

N-Mesityl-N′-[o-(o-mesitylaminooxalylaminophenoxymethyl)benzyloxyphenyl]-oxamide 3g. Buff crystals; yield 0.38 g (55%); mp 150–151 °C; ν_max(KBr)/cm⁻¹ 3358, 3295, 2952, 2920, 2861, 1685, 1647, 1600, 1509, 1479, 1452, 1380, 1253, 1202, 1113, 1011, 851, 750; δ_H(400 MHz, DMSO-d₆) 2.19 (s, 12H), 2.29 (s, 6H), 5.31 (s, 4H), 6.92 (s, 4H), 6.98–7.05 (m, 6H), 7.34–7.39 (m, 2H), 7.48–7.51 (m, 2H), 8.39 (d, 2H, J 8.4), 8.76 (s, 2H), 9.93 (s, 2H); δ_C(CDCl₃, 100 MHz) 18.5, 21.1, 69.1, 112.1, 119.9, 121.7, 125.6, 126.4, 129.0, 129.2, 129.3, 129.8, 134.3, 134.9, 137.8, 147.9, 157.4, 158.4; m/z (EI) 698 (M⁺); m/z (EI) 698.3099 (M⁺, C₄₂H₄₂N₄O₆ requires 698.3098).

Synthesis of diamine 2: general procedure

A solution of lithium aluminum hydride (0.5 g, 14 mmol) in dry diethyl ether (20 mL) was stirred for 5 min. Compound 3a–d (0.9 mmol) was added and the solution was refluxed for 4–24 h. After cooling to room temperature, the reaction mixture was quenched with water (0.5 mL), 15% aqueous NaOH (0.5 mL) and the ethereal solution was collected. After removal of the solvent in vacuo, the remaining mixture was crystallized from ethanol to give the corresponding amine derivatives 2a–c, 10. The mother liquor from crystallization of 2a was subjected to column chromatography using silica gel and elution with petroleum ether (40–60) and ethyl acetate to give compound 9.

Bis-ethane-1,2-diamine 2a. Colorless crystals; yield 0.38 g (78%); mp 83–85 °C; ν_max(KBr)/cm⁻¹ 3049, 3021, 2951, 2925, 2876, 2854, 1601, 1509, 1468, 1442, 1323, 1255, 1211, 1135, 1054, 741, 693; δ_H(400 MHz, CDCl₃) 2.26 (quint, 2H, J 6.0), 3.38 (s, 8H), 4.16 (t, 4H, J 6.0), 4.19 (br, 4H, NH), 6.60 (dd, 4H, J 8.0, 0.8), 6.67–6.74 (m, 6H), 6.79 (d, 2H, J 7.6), 6.90 (dt, 2H, J 1.6, 8.0), 7.17 (t, 4H, J 8.0); δ_C(CDCl₃, 100 MHz) 29.4, 43.3, 43.4, 63.4, 110.6, 111.1, 113.2, 117.3, 117.8, 121.8, 129.4, 138.2, 146.3, 148.1; m/z (EI) 496 (M⁺); m/z (EI) 496.2832 (M⁺, C₃₁H₃₆N₄O₂ requires 496.2833).

Bis-ethane-1,2-diamine 2b. Colorless crystals; yield 0.4 g (72%); mp 132–133 °C; ν_max(KBr)/cm⁻¹ 3372, 3350, 3046, 3021, 2947, 2937, 2876, 2882, 1601, 1508, 1468, 1442, 1323, 1258, 1211, 1133, 1054, 736, 690; δ_H(400 MHz, CDCl₃) 2.32 (quint, 2H, J 5.6), 3.36 (m, 8H), 3.74 (s, 6H), 4.18 (t, 4H, J 5.6), 4.67 (br, 4H, NH), 6.65 (dt, 2H, J 1.2, 7.6), 6.68 (d, 4H, J 8.8), 6.75–6.80 (m, 8H), 6.88 (dt, 2H, J 1.2, 7.6); δ_C(CDCl₃, 100 MHz) 29.4, 43.2, 44.7, 56.0, 65.4, 110.5, 111.2, 115.05, 115.08, 117.1, 121.8, 138.3, 141.7, 146.3, 152.8; m/z (EI) 556 (M⁺); m/z (EI) 556.3044 (M⁺, C₃₃H₄₀N₄O₄ requires 556.3050).

Bis-ethane-1,2-diamine 2c. Colorless crystals; yield 0.13 g (25%); mp 101–102 °C; ν_max(KBr)/cm⁻¹ 3399, 3034, 2919, 2875, 1601, 1516, 1469, 1444, 1254, 1218, 1131, 1051, 908, 809, 772, 738; δ_H(400 MHz, CDCl₃) 2.25 (s, 6H), 2.33 (t, 2H, J 6.0), 3.37–3.42 (m, 8H), 4.17 (t, 4H, J 6.0), 4.17 (br, 4H, NH), 6.63–6.71 (m, 8H), 6.79 (d, 2H, J 1.2, 6.8), 6.87 (dt, 2H, J 1.2, 7.6), 7.00 (d, 4H, J 8.4); δ_C(100 MHz, DMSO-d₆) 20.7, 29.5, 42.7, 45.6, 66.0, 110.7, 111.5, 115.5, 117.5, 121.8, 129.6, 130.0, 130.2, 138.0, 146.6; m/z (EI) 524 (M⁺); m/z (EI) 524.3146 (M⁺, C₃₃H₄₀N₄O₂ requires 524.3146).

N,N′-Diphenylethane-1,2-diamine 9a. Colorless solid; yield 0.05 g (10%); mp 63–65 °C (lit.¹⁶ mp 63–65 °C); δ_H(400 MHz, CDCl₃) 3.41 (s, 4H), 3.80 (br, 2H, NH), 6.68 (d, 4H, J 8.4), 6.76 (t, 2H, J 7.6), 7.22 (d, 4H, J 8.0); δ_C(CDCl3, 100 MHz) 43.4, 113.2, 118.0, 129.5, 148.2; m/z (EI) 212 (M⁺).

N-Mesityl-2-o-{3-[o-(mesitylcarbamoylmethylamino)phenoxy]propoxy}phenylamino-acetamide 10d. Colorless crystals; yield (0.45 g, 75%); mp 213–214 °C; ν_max(KBr)/cm⁻¹ 3270, 3064, 3035, 2954, 2920, 2879, 1650, 1602, 1513, 1485, 1463, 1450, 1446, 1260, 1218, 1129, 1063, 1054, 854, 734; δ_H(400 MHz, CDCl₃) 2.11 (s, 12H), 2.24 (s, 6H), 2.42 (quint, 2H, J 6.0), 3.96 (s, 4H), 4.28 (t, 4H, J 6.0), 4.99 (br, 2H, NH), 6.70 (dd, 2H, J 7.6, 1.2), 6.78 (dt, 2H, J 8.0, 1.2), 6.85 (s, 4H), 6.86 (m, 2H), 6.92 (dt, 2H, J 8.0, 1.2), 8.00 (s, 2H, NH); δ_C(CDCl₃, 100 MHz) 18.6, 21.1, 29.6, 49.1, 65.2, 110.9, 111.4, 119.0, 121.9, 129.1, 130.7, 135.2, 137.1, 137.2, 146.2, 169.4; m/z (EI) 608 (M⁺); m/z (EI) 608.3357 (M⁺, C₃₇H₄₄N₄O₄ requires 608.3357).

Synthesis of bis-imidazolinium salts 1a,b

Method A. HCl gas is passed for 20 min to diethylether and this solution was added to the above compound 2a (0.1 mmol) in ether. A solid forms and to this solid, triethylorthoformate (4 mL) was added and heated at 110 °C for 24 h. The triethylorthoformate was decanted and the product was washed with ether.

Method B. A mixture of the bisamine 2a,b (0.1 mmol), ammonium tetrafluoroborate (0.4 mmol), triethylorthoformate (4 mL), 2 drops of formic acid in toluene (10 mL) was heated under reflux for 24 h. The triethylorthoformate was decanted and the product was washed with ether.

Bis-imidazolinium 1a, X = Cl. Buff solid; yield 0.045 g (85%); mp 150–151 °C; ν_max(KBr)/cm⁻¹ 3336, 3045, 2930, 2884, 1674, 1620, 1591, 1498, 1460, 1270, 1222, 1124, 1045, 987, 958, 754; δ_H(400 MHz, DMSO-d₆) 2.35 (quint, 2H, J 6.0), 4.33 (t, 4H, J 6.0), 4.57 (s, 8H), 7.13 (t, 2H, J 7.6), 7.27 (d, 2H, J 7.6), 7.37 (t, 2H, J 7.2), 7.42 (t, 2H, J 7.6), 7.52 (t, 4H, J 7.6), 7.57 (d, 4H, J 7.6), 7.62 (dd, 4H, J 7.6, 1.2), 9.81 (s, 2H). δ_C(100 MHz, DMSO-d₆) 28.3, 48.3, 50.8, 65.8, 113.6, 118.1, 121.1, 124.7, 124.9, 126.9, 129.1, 130.0, 136.1, 151.5, 154.6; m/z (EI) 519.2754 (M⁺, C₃₃H₃₆³⁵Cl₂N₄O₂–HCl₂ requires 519.2754).

Bis-imidazolinium 1a, X = BF₄. Buff solid; yield 0.045 g (75%); mp 118–119 °C; ν_max(KBr)/cm⁻¹ 3335, 3079, 2952, 1676, 1627, 1592, 1548, 1499, 1437, 1290, 1262, 1223, 1053, 758. δ_H(400 MHz, DMSO-d₆) 2.35 (quint, 2H, J 6.0), 4.33 (t, 4H, J 6.0), 4.57 (s, 8H), 7.09–7.15 (m, 2H), 7.21–7.28 (m, 2H), 7.37–7.39 (m, 2H), 7.42 (t, 2H, J 7.6), 7.51–7.54 (m, 8H), 7.61 (d, 2H, J 7.6), 9.81 (s, 2H); δ_C(100 MHz, DMSO-d₆) 28.3, 48.4, 50.8, 65.8, 113.6, 118.1, 121.2, 124.8, 124.9, 127.0, 129.8, 130.1, 136.1, 151.5, 154.6; m/z (FAB) 606 (M⁺); m/z (EI) 606.2898 (M⁺, C₃₃H₃₆N₄O₂·BF₄ requires 606.2898).

Bis-imidazolinium 1b, X = BF₄. Buff powder; yield 0.05 g (82%); mp 142–143 °C; δ_H(400 MHz, DMSO-d₆) 2.35 (quint, 2H, J 6.0), 3.75 (s, 6H), 4.31 (t, 4H, J 6.0), 4.53 (s, 8H), 6.65–7.12 (m, 16H), 7.48 (d, 2H, J 9.2), 9.57 (s, 2H). δ_C(DMSO-d₆, 100 MHz) 28.9, 48.9, 50.6, 55.5, 65.7, 114.1, 119.9, 121.7, 123.7, 125.2, 129.1, 129.7, 138.4, 141.5, 145.8, 154.0; m/z (ESI) 666 (M⁺, C₃₅H₄₀N₄O₄·BF₄ requires 666).

Synthesis of diamine 11: general procedure

To a solution of lithium aluminum hydride (0.05 g, 14 mmol) in dry diethyl ether (2 mL) was added compound 3a,d (0.1 mmol) and the solution was heated at 110 °C in the microwave for 1 h. After cooling to room temperature, the reaction was quenched by adding H₂O (0.05 mL), 15% aqueous NaOH and small amount of water. The white precipitate was filtered and the product was extracted with ether to give compound 11.

N-Phenyl-N′-(2-propoxyphenyl)-ethane-1,2-diamine 11a. Buff precipitate; yield 0.21 g (80%); mp 69–70 °C; ν_max(KBr)/cm⁻¹ 3061, 3050, 3024, 2963, 2933, 2903, 2873, 1597, 1506, 1476, 1466, 1443, 1390, 1307, 1262, 1253, 1221, 1210, 1181, 1141, 1116, 1043, 1017, 906, 869, 745, 736, 692; δ_H(400 MHz, CDCl₃) 1.04 (t, 3H, J 7.4), 1.83 (sixtet, 2H, J 6.8), 3.44 (s, 4H), 3.96 (t, 2H, J 6.4), 4.34 (br, 2H, NH), 6.67 (dd, 2H, J 2.4, 8.0), 6.69–6.81 (m, 4H), 6.89 (dt, 1H, J 1.2, 7.6), 7.21 (tt, 2H, J 2.0, 8.0); δ_C(CDCl₃, 100 MHz) 10.8, 22.8, 43.26, 43.34, 69.1, 110.3, 110.8, 113.1, 117.1, 117.8, 121.3, 129.4, 138.1, 146.5, 148.2; m/z (EI) 270 (M⁺); m/z (EI) 270.1726 (M⁺, C₁₇H₂₂N₂O requires 270.1727).

N-Mesityl-N′-(2-propoxyphenyl)-ethane-1,2-diamine 11d. Colorless oil; yield 0.25 g (80%); δ_H(400 MHz, CDCl₃) 1.05 (t, 3H, J 7.2), 1.83 (sixtet, 2H, J 7.2), 2.23 (s, 3H), 2.27 (s, 6H), 3.22 (t, 2H, J 6.0), 3.36 (t, 2H, J 6.0), 3.96 (t, 2H, J 6.0), 4.14 (br, 2H, NH), 6.64–6.71 (m, 2H), 6.77–6.88 (m, 4H); m/z (EI) 312 (M⁺); m/z (EI) 312.2196 (M⁺, C₂₀H₂₈N₂O requires 312.2196).

Preparation of compound 13–18

A mixture of compound 4d (5.17 g, 2.2 mmol), diamine 12, substituted aniline (1 mmol) and boric acid (0.05 g) was heated at 180 °C for 1 h. The solid obtained was recrystallised from DMF to give product 13, 16a–c. To a solution of lithium aluminum hydride (0.05 g, 14 mmol) in dry diethyl ether (2 mL) was added compounds 13, 16a–c (0.1 mmol) and the solution was heated at 120 °C in the microwave for 1.5 h. After cooling to room temperature, the white precipitate was filtered off and the product was extracted with ether. Removal of the solvent in vacuo gave the corresponding amino derivatives 14, 17a–c which was used in the next step without further purification. HCl gas was passed for 20 min to ether and this ether solution was added to the above compound 14, 17a–c (0.25 g) in ether. A solid forms and to this solid, triethylorthoformate (4 mL) was added and heated at 110 °C for 24 h. Excess triethylorthoformate was decanted and the product obtained was washed with ether to give the corresponding imidazolidinium chloride 15, 18a–c.

N-Mesityl-N′-(4-{4-[(mesitylaminooxalyl)-amino]-benzyl}-phenyl)-oxamide 13. Colorless crystals; yield 0.34 g (60%); mp 294–295 °C; ν_max(KBr)/cm⁻¹ 3260, 3036, 2918, 2855, 1668, 1641, 1593, 1512, 1497, 1462, 1435, 1412, 1377, 1313, 1238, 1178, 1117, 1018, 847, 816, 787, 739; δ_H(400 MHz, DMSO-d₆) 2.12 (s, 12H), 2.25 (s, 6H), 3.91 (s, 2H), 6.92 (s, 4H),7.23 (d, 4H, J 8.4), 7.78 (d, 4H, J 8.4),10.29 (s, 2H, NH), 10.71 (s, 2H, NH); δ_C(DMSO-d₆, 100 MHz) 17.9, 20.5, 39.9, 120.6, 128.4, 128.9, 131.5, 134.8, 135.7, 136.1, 137.6, 158.4, 158.9; m/z (EI) 576 (M⁺); m/z (EI) 576.2731 (M⁺, C₃₅H₃₆N₄O₄ requires 576.2731).

N-Mesityl-N′-(4-{4-[2-(mesitylamino)-ethylamino]-benzyl}-phenyl)-1,2-ethanediamine 14. Colorless oil; yield 0.03 g (65%); ν_max(KBr)/cm⁻¹ 3371, 3005, 2941, 2916, 2853, 1614, 1578, 1518, 1483, 1468, 1437, 1410, 1319, 1308, 1254, 1231, 1217, 1180, 1130, 1103, 1030, 1013, 854, 808, 756; δ_H(400 MHz, CDCl₃) 2.25 (s, 12H), 2.28 (s, 6H), 3.21 (s, 4H), 3.36 (s, 4H), 3.80 (s, 2H), 3.87 (br, 4H, NH), 6.60 (d, 4H, J 8.0), 6.84 (s, 4H), 7.01 (d, 4H, J 8.0); δ_C(100 MHz, CDCl₃) 18.5, 20.7, 40.3, 44.6, 48.2, 113.4, 129.75, 129.77, 130.2, 131.4, 132.4, 142.2, 146.3; m/z (EI) 520 (M⁺); m/z (EI) 520.3560 (M⁺, C₃₅H₄₄N₄ requires 520.3560).

Bis-imidazolidinium dichloride 15. Green solid; yield 0.02 g (40%); mp 226–227 °C; ν_max(KBr)/cm⁻¹ 3028, 2974, 2917, 2860, 1659, 1624, 1603, 1512, 1497, 1479, 1294, 1265, 1227, 1026, 989, 856, 814, 785; δ_H(400 MHz, CDCl₃) 2.24 (s, 6H), 2.30 (s, 12H), 3.75 (s, 4H), 4.37 (s, 4H), 4.74 (s, 2H), 6.89 (s, 4H), 7.03 (d, 4H, J 8.0), 7.58 (d, 4H, J 8.0), 10.41 (s, 2H); δ_C(100 MHz, CDCl₃) 18.3, 21.3, 40.7, 49.5, 51.6, 119.0, 130.1, 130.3, 130.9, 134.1, 135.1, 139.9, 140.5, 156.4; m/z (EI) 542 (M⁺); m/z (EI) 541.3326 (M⁺, C₃₇H₄₂Cl₂N₄–HCl₂ requires 541.3325).

N-Phenyl-N′-mesityloxamide 16a. Colorless crystals; yield 0.028 g (86%); mp 239 °C; ν_max(KBr)/cm⁻¹ 3268, 3060, 3043, 3015, 2952, 2923, 2869, 1665, 1599, 1508, 1442, 1381, 1314, 1253, 1232, 1176, 1079, 1033, 877, 850, 782, 745, 711, 686. δ_H(400 MHz, CDCl₃) 2.22 (s, 3H), 2.30 (s, 6H), 6.94 (s, 2H), 7.22 (t, 1H, J 7.6), 7.39 (t, 2H, J 7.6), 7.68 (d, 2H, J 7.6), 8.86 (s, 1H), 9.38 (s, 1H); δ_C(CDCl₃, 100 MHz) 18.5, 21.1, 120.0, 125.6, 129.3, 129.37, 129.41, 129.8, 134.9, 136.6, 137.9, 157.7, 158.6; m/z (EI) 282.1363 (M⁺, C₁₇H₁₈N₂O₂ requires 282.1363).

N-(p-Methoxyphenyl)-N′-mesityloxamide 16b. Colorless crystals; yield 0.02 g (64%); mp 223–224 °C; ν_max(KBr)/cm⁻¹ 3330, 3294, 3001, 2955, 2921, 2834, 1669, 1612, 1597, 1511, 1495, 1467, 1440, 1414, 1379, 1304, 1247, 1230, 1172, 1112, 1034, 847, 825, 783, 769, 706. δ_H(400 MHz, CDCl₃) 2.21 (s, 3H), 2.30 (s, 6H), 3.82 (s, 3H), 6.88 (d, 2H, J 8.8), 6.94 (s, 2H), 7.60 (d, 2H, J 8.8), 8.90 (s, 1H), 9.37 (s, 1H); δ_C(CDCl₃, 100 MHz) 18.5, 21.1, 55.6, 114.5, 121.5, 129.3, 129.8, 129.9, 134.9, 137.8, 157.3, 157.4, 158.7; m/z (EI) 312.1468 (M⁺, C₁₈H₂₀N₂O₃ requires 312.1468).

N,N′-Bis-mesityloxamide 16c. Colorless crystals; yield 0.020 g (61%); mp 280–281 °C; ν_max(KBr)/cm⁻¹ 3197, 3006, 2975, 2919, 2876, 1671, 1535, 1489, 1459, 1443, 1389, 1258, 1035, 1019, 850, 801, 760, 703. δ_H(400 MHz, CDCl₃) 2.24 (s, 6H), 2.30 (s, 12H), 6.94 (s, 4H), 8.81 (s, 2H); δ_C(CDCl₃, 100 MHz) 18.6, 21.1, 129.2, 129.8, 134.8, 137.8, 158.4; m/z (EI) 324.1832 (M⁺, C₂₀H₂₄N₂O₂ requires 324.1832).

N-Mesityl-N′-phenyl-1,2-ethanediamine 17a (ref. 17). Colorless oil; yield 0.08 g (35%); ν_max(KBr)/cm⁻¹ 3402, 3050, 3019, 2997, 2943, 2916, 2855, 1603, 1505, 1484, 1431, 1321, 1255, 1230, 1213, 1179, 1154, 1124, 1029, 992, 855, 749, 692; δ_H(400 MHz, CDCl₃) 2.23 (s, 3H), 2.28 (s, 6H), 3.22 (t, 2H, J 5.6), 3.39 (t, 2H, J 5.6), 6.66 (d, 2H, J 8.4), 6.73 (t, 1H, J 7.6), 6.83 (s, 2H), 7.19 (t, 2H, J 7.6); δ_C(CDCl3, 100 MHz) 18.4, 20.6, 44.7, 47.8, 113.2, 117.8, 129.4, 129.6, 130.0, 131.8, 143.1, 148.3; m/z (EI) 254.1777 (M⁺, C₁₇H₂₂N₂ requires 254.1777).

N-Mesityl-N′-p-methoxyphenyl-1,2-ethanediamine 17b. Colorless oil; yield 0.017 g (60%); δ_H(400 MHz, CDCl₃) 2.29 (s, 3H), 2.31 (s, 6H), 3.22 (s, 2H), 3.32 (s, 2H), 3.40 (br, 2H, NH), 3.80 (s, 3H), 6.67 (d, 2H, J 8.8), 6.85 (d, 2H, J 8.8), 6.87 (s, 2H); δ_C(CDCl₃, 100 MHz) 18.5, 20.7, 45.5, 48.1, 55.9, 114.6, 115.0, 129.7, 130.2, 132.1, 142.4, 142.6, 152.5; m/z (EI) 284.1883 (M⁺, C₁₈H₂₄N₂O requires 284.1883).

N,N′-Dimesityl-1,2-ethanediamine 17c (ref. 12 and 17). Colorless oil; yield 0.22 g (75%); δ_H(400 MHz, CDCl₃) 2.23 (s, 6H), 2.28 (s, 12H), 3.15 (s, 4H), 6.87 (s, 4H); δ_C(CDCl3, 100 MHz) 21.4, 22.9, 50.4, 132.3, 133.3, 137.9, 138.7; m/z (EI) 296.2247 (M⁺, C₂₀H₂₈N₂ requires 296.2247).

1-Mesityl-3-phenyl-4,5-dihydro-1H-imidazolidinium chloride 18a. Colorless crystals; yield 0.014 g (55%); mp 293 °C; ν_max(KBr)/cm⁻¹ 2964, 2879, 1622, 1595, 1489, 1291, 1269, 754; δ_H(400 MHz, CDCl₃) 2.30 (s, 3H), 2.34 (s, 6H), 4.34 (t, 2H, J 10.4), 4.67 (t, 2H, J 10.4), 7.10 (s, 2H), 7.37 (t, 1H, J 7.6), 7.60–7.52 (m, 4H), 9.77 (s, 1H); δ_C(DMSO-d₆, 100 MHz) 17.3, 20.6, 48.5, 50.7, 118.0, 126.6, 129.4, 129.7, 131.2, 135.5, 136.2, 139.7, 156.1; m/z (FAB) 265 (M, C₁₈H₂₁N₂ requires 265).

1-Mesityl-3-p-methoxyphenyl-4,5-dihydro-1H-imidazolidinium chloride 18b. Colorless crystals; yield 0.012 g (42%); mp 267 °C; ν_max(KBr)/cm⁻¹ 3000, 2913, 2838, 1622, 1520, 1498, 1292, 1272, 1255, 1187, 1036, 831, 748; δ_H(400 MHz, CDCl₃) 2.26 (s, 3H), 2.34 (s, 6H), 3.79 (s, 3H), 4.36 (t, 2H, J 10.0), 4.72 (t, 2H, J 10.0), 6.90–6.96 (m, 4H), 7.72 (d, 2H, J 8.4), 10.49 (s, 1H); δ_C(CDCl₃, 100 MHz) 17.3, 20.6, 49.0, 50.6, 55.6, 114.7, 119.8, 120.0, 129.3, 131.2, 135.5, 139.5, 155.5, 157.9; m/z (FAB) 295 (M + 1, C₁₉H₂₃N₂O requires 295).

1,3-Bis-mesityl-4,5-dihydro-1H-imidazolidinium chloride 18c. Colorless crystals, yield 0.027 g (70%); mp 302–303 °C (lit.¹¹ mp > 250 °C); δ_H(400 MHz, CDCl₃) 2.26 (s, 6H), 2.35 (s, 12H), 4.53 (s, 4H), 6.91 (s, 4H), 9.31 (s, 1H); δ_C(CDCl₃, 100 MHz) 17.5, 20.8, 49.4, 50.9, 55.9, 115.1, 120.3, 129.7, 135.8, 155.7, 158.3.

Acknowledgements

Support from the University of Kuwait, received through Research Grant no. SC10/09 and facilities of GF-S (grant no. GS01/01, GS02/01, GS01/03, GS01/05) are gratefully acknowledged.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c4ra06128d

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