Ying
Cheng
*a,
Peng
Jiao
a,
David J.
Williams
b and
Otto-Meth
Cohn
*c
aChemistry Department, Beijing Normal University, Beijing, 100875, China. E-mail: Yincheng@public2.east.net.cn
bChemistry Department, Imperial College, London, UK SW7 2AY
cChemistry Department, University of Sunderland, Sunderland, UK SR1 3SD. E-mail: Otto.meth-cohn@sunderland.ac.uk
First published on 11th December 2000
2-Formamidopyridine in POCl3 solution reacts with N,N-dimethylaniline to give tris(4-dimethylaminophenyl)methane in 80% yield but with 4-X-N,N-dimethylanilines it gives 2-dimethylamino-5-X-phenyl[2-(N-methyl)formamido-5-X-phenyl](2-pyridylamino)methanes.
Scheme 1 |
Yields (%) | |||||
---|---|---|---|---|---|
3 X = | Ratio of 3∶6 | Time/h | Temp./°C | 7 | 8 |
a Under N2. | |||||
Me | 2∶1 | 8 | 80 | — | |
Me | 2∶1 | 20 | 75 | — | |
Me | 2∶1 | 17 | 94 | 25 | |
Me | 1∶1 | 18 | 96 | 47a | |
Me | 1∶2 | 18 | 96 | 57 | |
OMe | 2∶1 | 17 | 94 | 35 | |
OMe | 2∶1 | 8 | 100 | 32 | |
OMe | 1∶2 | 18 | 94 | 42 | |
F | 1∶1 | 36 | 90 | 44 | |
F | 1∶2 | 18 | 90 | 71 | |
Cl | 2∶1 | 18 | 90 | 34 | |
Cl | 1∶2 | 18 | 96 | 31 | |
Br | 2∶1 | 19 | 90 | 17 | |
Br | 1∶1 | 18 | 90 | 29 | |
Br | 1∶2 | 18 | 94 | 48 | |
Br | 1∶2 | 15 | 96 | 68 | |
H | 2∶1 | 18 | 90 | 80 |
Compound | Mp/°C | CHN% |
---|---|---|
a Lit.15 mp 177–178 °C. | ||
7a | 152–153 | C, 74.51; H, 7.33; N, 14.29. C24H28N4O requires C, 74.20; H 7.26; N, 14.42 |
7b | 153–154 | C, 68.63; H, 6.96; N, 13.16. C24H28N4O3 requires C, 68.55; H, 6.71; N, 13.32 |
7c | 169–171 | C, 66.59; H, 5.46; N, 14.02. C22H22F2N4O requires C, 66.48; H, 5.83; N, 14.10 |
7d | 195–197 | C, 61.52; H, 5.14; N, 12.82. C22H22Cl2N4O requires C, 61.40; H, 5.38; N, 13.02 |
7e | 182–184 | C, 51.27; H, 4.41; N, 10.55. C22H22Br2N4O requires C, 50.99; H, 4.28; N, 10.81 |
8 | 177–179a |
Cmpd. | IR (KBr) ν/cm−1 | 1H NMR (CDCl3) δ | 13C NMR (CDCl3) δ | MS m/z (%) |
---|---|---|---|---|
7a | 3280, 1660, 1600, 1480 | 8.05 (1H, d, J 4.2, CHO), 6.87–7.41 (7H, m), 6.57(1H, dd, J 5.4 and 2.7), 6.38 (1H, d, J 8.1), 6.22 (1H, d, J 8.1), 5.04 (1H, d, J 8.1, NH), 3.02 (3H, br s, NCH3), 2.67 (1H, s, NCH), 2.54 (6H, s, 2NCH3), 2.33 (3H, s, ArCH3), 2.21 (3H, s, ArCH3) | 161.8, 157.7, 149.9, 147.5, 142.0, 137.7, 137.2, 136.4, 132.1, 128.7, 128.4, 128.2, 128.1, 128.0, 120.1, 111.9, 108.7, 48.3, 44.7, 32.3, 20.9, 20.6 | 134 (62), 222 (56), 235 (62), 294 (100), 388 (85, M+), 389 (24) |
7b | 3380, 3260, 1680, 1600, 1500, 1480 | 8.0 (1H, d, J 4.8 CHO), 7.47 (1H, t, J 8.4), 7.17 (1H, d, J 8.7), 6.70–7.08 (5H, m), 6.63 (1H, t, J 5.7), 6.41 (1H, t, J 6.8), 6.34 (1H, d, J 8.5), 5.90 (1H, br s, NH), 3.76 (3H, s, OCH3), 3.71 (3H, s, OCH3), 3.06 (3H, br s, NCH3), 2.64 (1H, s, NCH), 2.50 (6H, s, 2NCH3) | 163.2, 162.6, 159.7, 156.5, 145.8, 142.1, 139.2, 137.7, 137.1, 133.1, 130.3, 122.5, 113.9, 113.3, 113.2, 112.8, 112.7, 107.2, 55.7, 51.1, 45.8, 33.4, 30.8 | 254 (58), 267 (70), 268 (54), 326 (100), 420 (51, M+), 421 (17) |
7c | 3300, 1680, 1620, 1500, 1480 | 8.01 (1H, d, J 4.7, CHO), 7.42 (1H, t, J 7.2), 6.94–7.27 (5H, m), 6.79 (1H, dd, J 9.3 and 2.9), 6.64 (1H, t, J 5.5), 6.50 (1H, d, J 6.4), 6.31 (1H, d, J 8.3), 5.27 (1H, d, J 6.3, NH), 3.07 (3H, s, NCH3), 2.65 (1H, s, NCH), 2.54 (6H, s, 2NCH3) | 164.2, 157.8, 156.8, 148.7, 147.9, 138.4/138.3, 138.0, 131.0/130.9, 122.8/122.7, 115.6, 115.4, 115.3, 115.1, 114.8, 114.5, 113.9, 113.5, 107.0, 50.5, 45.5, 33.1 | 124 (56), 136 (54), 138 (56), 230 (100), 243 (58), 302 (68), 396 (50, M+), 397 (13) |
7d | 3280, 1660, 1600, 1480 | 8.05 (1H, d, J 5.4, CHO), 7.52 (1H, d, J 2.7), 6.98–7.44 (6H, m), 6.62 (1H, dd, J 8.1 and 5.4), 6.52 (1H, d, J 8.1), 6.32 (1H, d, J 8.1), 4.92 (1H, d, J 5.4, NH), 3.03 (3H, s, NCH3), 2.67 (1H, s, NCH), 2.58 (6H, s, 2NCH3) | 162.1, 157.4, 151.6, 147.9, 144.3, 139.4, 138.9, 137.2, 133.1, 131.0, 128.4, 128.3, 128.2, 127.7, 127.5, 122.7, 113.0, 109.3, 48.7, 44.6, 32.7 | 154 (61), 246 (100), 334 (64), 428 (53)/430 (34)/432 (6) (M+) |
7e | 3300, 1680, 1610, 1490 | 8.03 (1H, d, J 4.8, CHO), 6.95–7.67 (7H, m), 6.65 (1H, t, J 5.6), 6.49 (1H, d, J 6.5), 6.25 (1H, d, J 6.0), 5.35 (1H, br s, NH), 3.03 (3H, s, NCH3), 2.67 (1H, s, NCH), 2.57 (6H, s, 2NCH3) | 117 (99), 290 (100), 292 (88), 405 (54), 407 (46), 424 (77), 516 (27)/518 (52)/520 (25) (M+) | |
8 | 1620, 1530 | 7.03 (6H, d, J 8.4), 6.91 (6H, d, J 7.7), 5.37 (1H, s, CH), 2.98 (18H, s, 6NCH3) | 252 (65), 253 (100), 254 (20), 372 (44), 373 (96, M+), 374 (26) |
Fig. 1 the X-ray structure of 7 (X = Cl).12 The principal intermolecular interaction is an N–H⋯O hydrogen bond between N(14) in one molecule and O(24) in the next [N⋯O, H⋯O distances 2.97, 2.27 Å, N–H⋯O angle 134°]. This interaction is supplemented by a weaker C–H⋯π interaction between C(10)–H in one molecule and the C(15) pyridyl ring of another [H⋯π distance 2.82 Å, C–H⋯π angle 151°]. |
Scheme 2 |
The formation of these surprising products involves an oxidation of one of the methyl groups of an N,N-dimethylaniline moiety, a process that we propose is initiated by a ‘t-amino effect’ interaction. A possible pathway is illustrated in Scheme 3. In fact, the reaction appears to require aerial oxidation for optimal yields. Nevertheless it does proceed under nitrogen. As noted in earlier work10 it is probable that iminium intermediates behave as dehydrogenating agents and hence the need for an excess of the pyridine amide. Addition of an oxidant, e.g. copper(II) acetate, does not improve yields.
Scheme 3 |
When N,N-dimethylaniline itself was treated with 2-formamidopyridine in POCl3 solution the reaction took a different course yielding tris(4-dimethylaminophenyl)methane 8 in high yield (80%). This well known compound, the precursor to ‘Crystal Violet’ (the tritylium salt thereof), has in fact been formed by, for example, the interaction of 4-dimethylaminobenzaldehyde with N,N-dimethylaniline and an acid13 or by treatment of a 4,4′-bis(dimethylamino)benzhydryl† derivative with N,N-dimethylaniline under acid catalysis.14 Similar benzaldehyde (i.e. an iminium salt derivative) and benzhydryl analogues can be easily formed in our case to account for this efficient reaction. It is of interest that while classical Vilsmeier reagents with N,N-dimethylaniline yield solely 4-formyldimethylaniline, this reagent proceeds further, due to the greater formylating ability of the derived iminium ion (cf. Scheme 3). When the iminium intermediate of the formylation of N,N-dimethylaniline with DMF–POCl3 is reacted with further N,N-dimethylaniline, the same triarylmethane is formed.15
Footnote |
† The IUPAC name for benzhydryl is diphenylmethyl. |
This journal is © The Royal Society of Chemistry 2001 |