Catalytic synthesis of homoallyloxyalcohols and 1,2-bis(homoallyloxy)ethanes through ring-opening allylation of cyclic acetals with allylsilanes over solid acids

Abstract

Ring-opening allylation of cyclic acetals with allylsilanes afforded silyl ethers using a silica–alumina catalyst. For example, the reaction of 2-phenyl-1,3-dioxolane with allyltrimethylsilane gave the corresponding silyl ether in 83% yield. After the allylation, addition of water to the reaction mixture allowed hydrolysis of the silyl ether to afford the homoallyloxyalcohol in 77% yield based on the acetal used. The reaction pathway of the silica–alumina-catalyzed allylation was examined. Solid-state ¹³C and ²⁹Si NMR analyses revealed the generation of SiMe₃ groups on the silica–alumina surface. The part of the (surface)–O–SiMe₃ groups was found to be an active site for the allylation reaction. During the silica–alumina-catalyzed allylation, a small amount of 1,2-bis(homoallyloxy)ethane formed as a co-product. The selectivity toward the 1,2-bis(homoallyloxy)ethane increased from 7% to 60% using H⁺-montmorillonite instead of silica–alumina. Detailed reaction pathways for the syntheses of 1,2-bis(homoallyloxy)ethanes were also investigated.

---

Introduction

Allylation of acetals is promoted by acid reagents.^1,2 However, a stoichiometric amount of Lewis acid to the acetal is necessary for ring-opening allylation of cyclic acetals.² To obtain the homoallyloxyalcohol by the Lewis acid-promoted ring-opening allylation, water or an alcohol can be added to decompose the “Lewis acid-allylation product complex (alkoxide)” (Scheme 1, path A).² It was reported that a catalytic amount of a Lewis acid did not show good performance for the ring-opening allylation of cyclic acetals.³ The reason for this seems to be that the Lewis acidic species is not regenerated after the allylation. To regenerate a catalytically active species, acid anhydrides were used as additives to afford ester products instead of the homoallyloxyalcohols (Scheme 1, path A (dotted line)).³ It is believed that the acid anhydride captures the “Lewis acid-allylation product complex”.

Scheme 1 Lewis acid-promoted ring-opening allylation of cyclic acetal (path A) and catalytic synthesis of homoallyloxyalcoholvia introduction of a leaving group (LG) to ring-opened acetal (path B).

If a leaving group (LG) of the allylating reagent is introduced to the allylation product, regeneration of the promoter connected to the ring-opened acetal should be unnecessary (Scheme 1, path B). It means the catalytic ring-opening allylation of the cyclic acetal can proceed. It can be expected that an interaction between the cyclic acetal and the leaving group during the allylation creates the possibility of introducing the leaving group to the allylation product.

It is well known that Si species acts as Lewis acid sites for several nucleophilic addition reactions, including allylation.⁴ These active Si species can be generated by the reaction between an allylsilane and a Brønsted acid.⁵ These facts encouraged us to use allylsilane as an allylating reagent and a Brønsted acid as an initiator of the Si species for the ring-opening allylation of cyclic acetals. Herein, we report the catalytic ring-opening allylation of cyclic acetals with allylsilanes using silica–alumina as a solid acid. The ring-opening allylation afforded silyl ethers that can be hydrolyzed to homoallyloxyalcohols in the presence of the silica–alumina (eqn (1)).⁶ In addition, 1,2-bis(homoallyloxy)ethane, a potentially useful compound with many functional groups, formed as a co-product during the allylation. The selectivity toward the 1,2-bis(homoallyloxy)ethane increased with an H⁺-montmorillonite catalyst (eqn (2)). Detailed reaction pathways of the catalytic ring-opening allylation and 1,2-bis(homoallyloxy)ethane synthesis were also investigated.

Results and discussion

Ring-opening allylation over Brønsted acids

Ring-opening allylations of 2-phenyl-1,3-dioxolane (1a) with 1.2 equivalents of allyltrimethylsilane (2a) in the presence of heterogeneous inorganic acids were carried out at 60 °C. The results are summarized in Table 1. An 81% yield of the ring-opened allylation product (3aa) could be achieved with silica–alumina (entry 1). 1,2-Bis(homoallyloxy)ethane (4aa) formed as a by-product in 7% yield. H⁺-beta also showed catalytic activity to afford 43% yield of 3aa (entry 2). Other zeolites used, such as H⁺-mordenite and H⁺-USY, showed much lower performances under the reaction conditions (entries 3–6). These results suggest that the higher accessibility of substrates to the active site on amorphous silica–aluminaversus other zeolites induces the higher performance of silica–alumina.

Table 1 Ring-opening allylation of 2-phenyl-1,3-dioxolane (1a) with allyltrimethylsilane (2a) using Brønsted acids^a

Entry	Acid (SiO2/Al2O3)	Conv. of 1a^b (%)	Conv. of 2a^b (%)	Yield^b (%)
				3aa ^c	4aa ^d
a Reaction conditions: 1a (3.7 mmol), 2a (4.4 mmol), acid (0.05 g), toluene (3.0 mL), 60 °C, Ar atmosphere, 27 h. b Determined by GC using an internal standard. c Yield based on acetal 1a. d Yield = [4aa (mmol) × 2/1a (mmol)] × 100. e 0.15 g of zeolite was used.
1	Silica–alumina (6.3)	95	94	81	7
2	H^+-Beta (25)	75	86	43	3
3^e	H^+-Mordenite (18)	42	56	8	<1
4^e	H^+-USY (5.9)	24	52	1	1
5^e	H^+-ZSM-5 (23.8)	24	33	<1	<1
6	FSM-16	25	45	18	2
7	Amorphous SiO2	4	37	<1	<1
8	Na–silica–alumina	11	40	1	<1

---

An 18% yield of 3aa was obtained with mesoporous silica FSM-16 (entry 6),⁷ however, amorphous SiO₂ did not show catalytic activity (entry 7). It can be said that the Si–OH group did not act as an active site for the allylation. To confirm the role of the Brønsted acid site of silica–alumina, the allylation using silica–alumina treated with NaOH/NaCl solution (Na–silica–alumina) was examined. The reaction afforded only 1% yield of 3aa (entry 8). These results indicate that the acid site on the silica–alumina acts as a catalytically active site for the allylation, because the amount of acid site on the silica–alumina is estimated to be 0.154 mmol g⁻¹ by NH₃-TPD analysis.

Reaction time and solvent were optimized in the silica–alumina-catalyzed allylation of 1a with 2a, as shown in Table 2. It was expected that strong electron donation from solvent molecules would decrease the activity of the acid site. To determine the effect of solvent polarity on the catalytic performance, the dielectric values ε of the solvents as a criterion of polarity are also listed. An 83% yield of 3aa was obtained after 8 h with toluene (entry 3). n-Heptane and 1,4-dioxane also acted as good solvents (entries 5 and 6), whereas acetonitrile, 2-propanol, and DMF were substantially less active (entries 7–9). These results suggest that nonpolar solvents with low dielectric constants are good media for the ring-opening allylation. The active Brønsted acid site on silica–alumina can be deactivated by the electron donating effect of highly polar solvents.⁸

Table 2 Silica–alumina-catalyzed ring-opening allylation of 2-phenyl-1,3-dioxolane (1a) with allyltrimethylsilane (2a) under various conditions^a

Entry	Solvent [dielectric constant (ε)]	Time/h	Conversion of 1a^b (%)	Yield^b (%)
				3aa ^c	4aa ^d
a Reaction conditions: 1a (3.7 mmol), 2a (4.4 mmol), silica–alumina (0.05 g), solvent (3.0 mL), 60 °C, Ar atmosphere. b Determined by GC using an internal standard. c Yield based on acetal 1a. d Yield = [4aa (mmol) × 2/1a (mmol)] × 100.
1	Toluene (2.4)	1	40	38	4
2	Toluene (2.4)	3	75	67	6
3	Toluene (2.4)	8	95	83	7
4	Toluene (2.4)	27	95	81	7
5	n-Heptane (1.9)	27	96	76	12
6	1,4-Dioxane (2.2)	27	90	76	13
7	Acetonitrile (37.5)	27	15	3	1
8	2-Propanol (18.6)	27	36	<1	<1
9	DMF (36.7)	27	<1	<1	<1

---

Ring-opening allylation of 1a with other allylsilanes proceeded as shown in Scheme 2. The reactions with methallyltrimethylsilane, crotyltrimethylsilane, and allyltriethylsilane afforded the corresponding allylated products in 76, 52, and 50% yields, respectively.

Scheme 2 Silica–alumina-catalyzed ring-opening allylation using various allylsilanes.

Reaction pathways of ring-opening allylation

It is reported that reactions between the surface H⁺ site or Si–OH group and allylsilane give (surface)–O–SiR₃ groups and propylene.^5,9Scheme 3 shows possible reaction pathways for the allylation involving (surface)–O–SiR₃ group formation [Scheme 3(A)]. Here, Si¹ and Si² are the SiR₃ group on the silica–alumina surface and the SiR₃ group in the allylsilane, respectively. As shown in Scheme 3(B), the surface Si species (Si¹) might be introduced to the cyclic acetal, and then nucleophilic addition of the allyl group of the allylsilane occurs. The surface Si species (Si²) is regenerated by the Si group in the allylsilane. To confirm this reaction pathway, the following experiments were conducted. The reaction of an excess amount of allyltrimethylsilane (2a) with silica–alumina afforded propylene and SiMe₃-functionalized silica–alumina (SiMe₃–silica–alumina) (Scheme 4). The solid-state ²⁹Si and ¹³C CP/MAS NMR spectra of the SiMe₃–silica–alumina are shown in Fig. 1(A) and 2(A), respectively. Signals at around 14 ppm in the ²⁹Si NMR spectrum and 0 ppm in the ¹³C NMR spectrum clearly indicate the presence of (surface)–O–SiMe₃ groups on silica–alumina.¹⁰ Next, the reaction of acetal (1a) and allyltriethylsilane (2b) in the presence of the SiMe₃–silica–alumina was carried out. The result is shown in Scheme 5. Formation of 1% yield of the ring-opened allylation product with a SiMe₃ group was detected.¹¹ After the reaction of 1a, 2b, and SiMe₃–silica–alumina, the silica–alumina was recovered and solid-state NMR measurements were conducted [Fig. 1(B) and 2(B)]. As shown in Fig. 2(B), a new signal at around 5.4 ppm was detected in the ¹³C NMR spectrum. This indicates the presence of a (surface)–O–SiEt₃ group on the silica–alumina after the allylation with 2b.¹² These reaction and NMR results strongly support the allylation pathway involving Si exchange [Scheme 3(B)]. After the reaction with 2b, the 0 ppm signal still remained in the ¹³C NMR spectrum [Fig. 2(B)]. This result indicates the existence of an inactive (surface)–O–SiMe₃ group on the silica–alumina. Because amorphous SiO₂ had no catalytic activity (Table 1, entry 8), the inactive species might be the Si–O–SiMe₃ generated from the simple Si–OH group and 2a, as shown in Scheme 6A. It is suggested that the catalytically active Si species on the silica–alumina was generated by the reaction between the Brønsted acid site due to the [Si–O(H⁺)–Al] moiety and 1a (Scheme 6B).

Scheme 3 Formation of Si species on the silica–alumina surface (A) and possible reaction pathways of ring-opening allylation involving: (B) Si exchange reaction and (C) intramolecular addition of Si species via a 6-membered transition state. Si¹ and Si² are trialkylsilyl species such as SiMe₃.

Scheme 4 Formation of SiMe₃ species on silica–alumina.

Fig. 1 Solid-state ²⁹Si CP/MAS NMR for (A) SiMe₃–silica–alumina, and (B) recovered SiMe₃–silica–alumina after the reaction with 1a and 2b. The signals at around −107 ppm are assignable to bulk Si in silica–alumina.

Fig. 2 Solid-state ¹³C CP/MAS NMR for (A) SiMe₃–silica–alumina, and (B) recovered SiMe₃–silica–alumina after the reaction with 1a and 2b.

Scheme 5 Reaction of SiMe₃–silica–alumina with 1a and allyltriethylsilane (2b).

Scheme 6 Proposed reaction pathway involving formation of both active and inactive SiMe₃ species on the silica–alumina surface.

If the allylation proceeds via the reaction pathway involving the Si exchange reaction [Scheme 3(B)], four types of allylation products should form by cross-allylation of 1a in the presence of both methallyltrimethylsilane (methallyl–SiMe₃) and allyltriethylsilane (allyl–SiEt₃). The cross-allylation was carried out, as shown in Scheme 7. According to our expectations, four types of allylation products including allyl–SiMe₃ groups and methallyl–SiEt₃ groups were obtained. This result supports the reaction pathway including Si transfer [Scheme 3(B)]. However, these results cannot completely exclude a concerted mechanism through a 6-membered ring transition state [Scheme 3(C)], which was reported in the allylation of carbonyl compounds using allylsilanes.^4,13 The presence of both reaction pathways is possible in the ring-opening allylation using silica–alumina.

Scheme 7 Ring-opening allylations of 1a in the presence of both methallyltrimethylsilane and allyltriethylsilane.

Hydrolysis of silyl ethers

After the allylation of acetals (1) with 2a using silica–alumina, water was added to the reaction mixture. Hydrolysis of the silyl ethers (3) occurred to afford homoallyloxyalcohols (5). These results are summarized in Table 3. In the case of acetal 1a, the corresponding homoallyloxyalcohol (5aa) was obtained in 77% yield after 23 h (entry 3). The recovered silica–alumina was calcined at 500 °C, and then reused for the allylation–hydrolysis sequence. A 70% yield of 5aa was obtained after a prolonged reaction time for the allylation (entry 4). The hydrolysis reaction scarcely proceeded in the absence of the silica–alumina (entry 5). This result suggests that hydrolysis of 3 was promoted by the silica–alumina. The silica–alumina catalyst was also applicable toward other ethylene acetals, such as 2-methyl-1,3-dioxolane (1c) and simple 1,3-dioxolane (1d), affording 51–77% yields of homoallyloxyalcohols (entries 6–11). In the case of acetals with small sizes, the product selectivity in the allylation step was moderate due to the formation of the bis(homoallyloxy)ethane (4) as a by-product. Reaction of 2-phenyl-4-methyl-1,3-dioxolane (1h) afforded both primary and secondary alcohols (entry 12). 1,3-Dioxane (1i) also reacted with 2a to give the corresponding homoallyloxyalcohol (entry 13). Allylation of ethylene ketal, such as 2,2-dimethyl-1,3-dioxolane, hardly proceeded in the reaction conditions.

Table 3 Silica–alumina-catalyzed homoallyloxyalcohol (5) synthesis from cyclic acetals (1) and allyltrimethylsilane (2a)^a

Entry	Acetal (1)	Time/h		Product (5)	Yield of 5^b (%)
		Allylation	Hydrolysis
a Reaction conditions: [allylation] acetal 1 (3.7 mmol), 2a (4.4 mmol), silica–alumina (0.05 g), toluene (3.0 mL), 60 °C, Ar atmosphere. [hydrolysis] water (11 mmol), acetone (3.0 mL), 25 °C. b Determined by GC using an internal standard. Yield based on acetal 1. c Reuse experiment. d Result of hydrolysis reaction of allylation product 3aa in the absence of silica–alumina. e Silica–alumina (0.10 g) was used. f Isolate yield. g A mixture of 1 ∶ 1 diastereoisomers was obtained. Product structures and ratio were determined by ^1H and ^13C NMR, H–H COSY, C–H COSY, and H–H NOESY.
1		8	3		45
2	1a	8	6	5aa	63
3	1a	8	23	5aa	77
4	1a	20	23	5aa	70^c
5	1a	—	3	5aa	3^d
6		8	8		77
7		27	27		60
8		27	27		68
9		27	3		51
10		14	20		51^ef
11		14	20		58^e^,^f
12		20	6		59^e^,^f^,^g
					14^e^,^f^.^g
13		22	6		53^f

---

1,2-Bis(homoallyloxy)ethane synthesis and reaction pathway

During the above ring-opening allylation of cyclic acetals with allylsilanes, we detected the formation of small amounts of 1,2-bis(homoallyloxy)ethane (4aa). The 1,2-bis(homoallyloxy)ethane structure might have potentially utility for organic synthesis and polymer chemistry because of its two terminal C=C bonds and ether functions. Only one example was reported for the synthesis of 4aa from a diphenyl dioxane using an electrochemical procedure.¹⁴ Our solid acid-catalyzed approach toward 4aa has the following advantages: (i) readily available cyclic acetals can be used as substrates, (ii) various functional groups can be introduced by choosing appropriate acetal structures. These facts encouraged us to investigate efficient procedures for 1,2-bis(homoallyloxy)ethane synthesis.

Because of the larger size of 4aa than 3aa, homogeneous acids and heterogeneous acids, which can be used for transformation of large substrates,¹⁵ are thought to be effective to increase the yield of 4aa. Among these acid catalysts, montmorillonite was reported by Kaneda and co-workers as a highly efficient heterogeneous acid catalyst for reactions of large molecules, such as BHEPF, 1,3-diphenyl-2-propanone, and steroid.^15a–c These catalysts were employed in the reaction of 1a with 2a. The results are summarized in Table 4. The reaction using H⁺-montmorillonite as a solid acid afforded 4aa in up to 60% yield (entry 2). Nafion and Amberlyst also showed higher selectivity toward 4aa than 3aa (entries 3 and 4), however, the yield of 4aa was lower than with the H⁺-montmorillonite. A 35% yield of 4aa was obtained with homogeneous trifluoromethane sulfonic acid (CF₃SO₃H) (entry 6). The reaction hardly proceeded with other homogeneous acids used, such as p-toluenesulfonic acid and H₂SO₄.

Table 4 Synthesis of 4aa from 2-phenyl-1,3-dioxolane (1a) with allyltrimethylsilane (2a) using acids^a

Entry	Acid	t/h	Conversion of 1a^b (%)	Yield^b (%)
				3aa ^c	4aa ^d
a Reaction conditions: 1a (3.7 mmol), 2a (4.4 mmol), acid (0.05 g), toluene (3.0 mL), 60 °C, Ar atmosphere. b Determined by GC using an internal standard. c Yield based on acetal 1a. d Yield = [4aa (mmol) × 2/1a (mmol)] × 100. e The reaction of 1a (3.7 mmol) and 2a (3.7 mmol) was carried out for 8 h. Then, 2a (0.7 mmol) was added, and the reaction was conducted for an additional 2 h. f CF3SO3H (0.18 mmol).
1	H^+-Montmorillonite	4	>95	19	56
2^e	H^+-Montmorillonite	10	>99	23	60
3	Nafion	28	90	31	48
4	Amberlyst	24	64	25	42
5	SO4/ZrO2	6	41	32	17
6	CF3SO4H ^f	1	79	8	35

---

1,2-Bis(homoallyloxy)ethane synthesis from 2-methyl-1,3-dioxolane (1c) and 4-methyl-2-phenyl-1,3-dioxolane using H⁺-montmorillonite were carried out, as shown in Scheme 8. A 54% yield of the corresponding product formed from 2-methyl-1,3-dioxolane (1c). In the reaction of the 4-methyl-2-phenyl-1,3-dioxolane, the presence of a methyl group in the product clearly indicates that the 1,2-bis(homoallyloxy)ethane was constructed with one protecting group of the acetal.

Scheme 8 Reaction of 2-methyl-1,3-dioxolane (1c) and 4-methyl-2-phenyl-1,3-dioxolane with allyltrimethylsilane (2a) using H⁺-montmorillonite.

To reveal the reaction pathway for the 1,2-bis(homoallyloxy)ethane formation, silyl ether (3aa) was treated with H⁺-montmorillonite at 60 °C. Only 4% yield of 4aa was obtained (Scheme 9). This result indicates that the dimerization of 3aa is not a main pathway toward 4aa. Next, the conversion of 3aa using H⁺-montmorillonite in the presence of 1c and 2a was performed, as shown in Scheme 10. 1,2-Bis(homoallyloxy)ethane having both phenyl and methyl groups (4ca) was obtained in 38% yield along with 1% yield of 4aa. From this result, the main reaction pathway toward 1,2-bis(homoallyloxy)ethane from acetal and allylsilane is proposed as follows: (i) acetal exchange reaction¹⁶ of a silyl ether 3 with an acetal 1, (ii) nucleophilic addition of allylsilane 2 to the acetal intermediate, (iii) formation of 1,2-bis(homoallyloxy)ethane 4 along with bis(trimethylsiloxy)ethane (Scheme 11). The formation of bis(trimethylsiloxy)ethane during the H⁺-montmorillonite-catalyzed reaction supports this reaction pathway.

Scheme 9 Reaction of 3aa using H⁺-montmorillonite.

Scheme 10 Reaction of ring-opening allylation product 3aa in the presence of acetal 1c and allyltrimethylsilane 2a using H⁺-montmorillonite.

Scheme 11 Proposed reaction pathway for 4.

Conclusion

We have found that silica–alumina acts as an efficient heterogeneous catalyst for the ring-opening allylation of cyclic acetals with allylsilanes. The corresponding homoallyloxyalcohols formed after silica–alumina-catalyzed allylation/hydrolysis sequences. An active (surface)–O–SiR₃ group was generated on silica–alumina by the reaction between the Brønsted acid site [Si–O(H⁺)–Al] and the allylsilane. The catalytic allylation pathway involving the formation of a (surface)–O–SiR₃ group on silica–alumina followed by Si transfer has been proposed for the present ring-opening allylation. In addition, good yields of 1,2-bis(homoallyloxy)ethanes could be obtained from cyclic acetals and allylsilane using H⁺-montmorillonite instead of silica–alumina.

Experimental section

Proton (¹H) and carbon (¹³C) nuclear magnetic resonance (NMR) spectra were recorded in CDCl₃ with a JNM-AL300 spectrometer operating at 300 and 75 MHz, respectively. Analytical GLC was measured using a Shimadzu GC-8A equipped with a Silicon SE-30 and OV-17 column and a thermal conductivity (TCD) detector. A Shimadzu QP5000 equipped with DB-1 column was used as GC-MS. The products were confirmed by comparison with reported NMR and MS data. Solid-state ¹³C and ²⁹Si CP/MAS NMR spectra (MAS rate = 5 kHz) were recorded with an AVANCE III spectrometer operating at 100.6 and 79.5 MHz, respectively. Cross-polarization (CP) contact times of ¹³C and ²⁹Si CP/MAS NMR measurements were 0.5 and 10.0 ms, respectively. The accumulation number and delay time were about 100 000 and 1.0 s (¹³C), and 2500 and 4.0 s (²⁹Si), respectively. Adamantane (δ 38.52 and 29.47 ppm) and hexamethylcyclotrisiloxane (δ −9.66 ppm) were used as external standards for the calibration of chemical shifts.

Silica–alumina was available from Nikki Chemical Co. as N633L (SiO₂, 80.6, Al₂O₃, 12.8 wt%, 408 m² g⁻¹). H⁺-montmorillonite was prepared from Na⁺-montmorillonite (Knipia F) using an ion exchange procedure with aqueous hydrogen chloride.¹⁷H⁺-beta (SiO₂/Al₂O₃ = 25), H⁺-mordenite (SiO₂/Al₂O₃ = 18.0), and H⁺-USY (SiO₂/Al₂O₃ = 5.9) were purchased from Nikki Chemical Co. H⁺-ZSM-5 (SiO₂/Al₂O₃ = 23.8) was obtained from Toso Co. FSM-16 was obtained from Fuji Silysia Chemical Co. Aerosil 300 was used as amorphous SiO₂. SO₄/ZrO₂ was purchased from Japan Energy Co. (S content: 3.2 wt%). These inorganic solid acids, except for H⁺-montmorillonite, were treated at 500 °C under air and 120 °C under vacuum before use. Amberlyst was purchased from Organo Co. as Amberlyst® 15DRY. Nafion was purchased from Aldrich Inc. as Nafion® NR50. Na–silica–alumina (Na content: 4.7 wt%) was prepared from silica–alumina using an ion exchange procedure with 1 M NaCl solution at 80 °C for 3 h. The pH of the solution was adjusted to 9 by addition of aqueous NaOH solution. After the treatment, the solid was filtered, washed with deionized water, then dried at 110 °C. Unless otherwise noted, other materials were purchased from Wako Pure Chemicals, Tokyo Kasei Co., Kanto Kagaku Co. and Aldrich Inc.

Ring-opening allylation

Into a glass reactor were placed silica–alumina (0.05 g), toluene (3.0 mL), 1a (3.7 mmol), and 2a (4.4 mmol) under a dry Ar atmosphere. The resulting mixture was vigorously stirred at 60 °C. After 27 h, the catalyst was separated by filtration and GC analysis of the filtrate showed an 81% yield of the allylated product 3aa and 7% yield of 4aa. The filtrate was evaporated and the crude product was purified by column chromatography using silica (n-hexane/ether = 9/1) to afford pure products 3aa and 4aa.

Hydrolysis of silyl ether

After the ring-opening allylation using silica–alumina, water (0.2 mL, 11 mmol) and acetone (3.0 mL) were added to the same flask. The resulting mixture was vigorously stirred at 25 °C for 3 h. The catalyst was separated by filtration and GC analysis of the filtrate showed a 77% yield of homoallyloxyalcohol 5aa. The filtrate was evaporated and the crude product was purified by column chromatography using silica (n-hexane/ether = 9/1 to 1/1) to afford pure product 5aa.

Acknowledgements

This work was supported by a Grant-in-Aid for Young Scientists (B) (Grant No. 21760626) and The Noguchi Institute (NJ200909). This study was also supported by the Cooperative Research Program of Catalysis Research Center (CRC), Hokkaido University. (Grant No. 10B2006). K.M. thanks Prof. Kenji Hara (CRC, Hokkaido University) and Prof. Atsushi Fukuoka (CRC, Hokkaido University). The authors thank Center for Advanced Materials Analysis (Suzukakedai), Technical Department, Tokyo Institute of Technology, for NMR and elemental analysis.

References

1. Allylation of acyclic acetals: (a) A. Hosomi, M. Endo and H. Sakurai, Chem. Lett., 1976, 941; (b) A. Hosomi, M. Endo and H. Sakurai, Chem. Lett., 1978, 499; (c) H. Sakurai, K. Sasaki, J. Hayashi and A. Hosomi, J. Org. Chem., 1984, 49, 2808; (d) T. Mukaiyama, H. Nagaoka, M. Murakami and M. Ohshima, Chem. Lett., 1985, 977; (e) M. Kawai, M. Onaka and Y. Izumi, Chem. Lett., 1986, 381; (f) N. Komatsu, M. Uda, H. Suzuki, T. Toshikazu, T. Domae and M. Wada, Tetrahedron Lett., 1997, 38, 7215; (g) L. C. Wieland, H. M. Zerth and R. S. Mohan, Tetrahedron Lett., 2002, 43, 4597; (h) H. M. Zerth, N. M. Leonard and R. S. Mohan, Org. Lett., 2003, 5, 55.
2. Allylation of cyclic acetals: (a) P. A. Bartlett, W. S. Johnson and J. D. Elliott, J. Am. Chem. Soc., 1983, 105, 2088; (b) W. S. Johnson, P. H. Crackett, J. D. Elliott, J. J. Jagodzinski, S. D. Lindell and S. Natarajan, Tetrahedron Lett., 1984, 25, 3951; (c) Y. Yamamoto, S. Nishii and J.-I. Yamada, J. Am. Chem. Soc., 1986, 108, 7116; (d) S. E. Denmark and N. G. Almstead, J. Am. Chem. Soc., 1991, 113, 8089; (e) S. E. Denmark and N. G. Almstead, J. Org. Chem., 1991, 56, 6458; (f) T. Sammakia and R. S. Smith, J. Am. Chem. Soc., 1992, 114, 10998; (g) T. Sammakia and R. S. Smith, J. Org. Chem., 1992, 57, 2997; (h) S. Jiang, G. E. Agoston, T. Chen, M.-P. Cabal and E. Turos, Organometallics, 1995, 14, 4697; (i) Y. Egami, M. Takayanagi, K. Tanino and I. Kuwajima, Heterocycles, 2000, 52, 583; (j) S. Bogaczyk, M.-R. Brescia, Y. C. Shimshock and P. DeShong, J. Org. Chem., 2001, 66, 4352; (k) F. Carrel, S. Giraud, O. Spertini and P. Vogel, Helv. Chim. Acta, 2004, 87, 1048; (l) G. K. Friestad and H. J. Lee, Org. Lett., 2009, 11, 3958.
3. M. J. Spafford, J. E. Christensen, M. G. Huddle, J. R. Lacey and R. S. Mohan, Aust. J. Chem., 2008, 61, 419.
4. (a) Y. Yamamoto and N. Asao, Chem. Rev., 1993, 93, 2207; (b) J. Beignet, P. J. Jervis and L. R. Cox, J. Org. Chem., 2008, 73, 5462.
5. (a) A. P. Davis and M. Jaspars, J. Chem. Soc., Chem. Commun., 1990, 1176; (b) K. Higuchi, M. Onaka and Y. Izumi, Bull. Chem. Soc. Jpn., 1993, 66, 2016.
6. K. Motokura, H. Yoneda, A. Miyaji and T. Baba, Green Chem., 2010, 12, 1373.
7. Effects of mesoporous structures on acid-catalyzed reactions have been reported by Iwamoto and co-workers: (a) M. Iwamoto, Y. Tanaka, N. Sawamura and S. Namba, J. Am. Chem. Soc., 2003, 125, 13032; (b) H. Ishitani, H. Naito and M. Iwamoto, Catal. Lett., 2008, 120, 14.
8. K. Motokura, M. Tomita, M. Tada and Y. Iwasawa, Chem.–Eur. J., 2008, 14, 4017.
9. (a) T. Shimada, K. Aoki, Y. Shinoda, T. Nakamura, N. Tokunaga, S. Inagaki and T. Hayashi, J. Am. Chem. Soc., 2003, 125, 4688; (b) K. Aoki, T. Shimada and T. Hayashi, Tetrahedron: Asymmetry, 2004, 15, 1771.
10. D. Derouet and C. N. Ha Thuc, J. Appl. Polym. Sci., 2008, 109, 2113.
11. The amount of acid sites in 0.20 g silica–alumina is estimated to be 3.1 × 10⁻² mmol from NH₃-TPD results. This value is larger than that for the SiMe₃-containing allylation product (4.0 × 10⁻³ mmol). The amount of active H⁺ sites for the allylation might be lower than the acid sites determined by NH₃-TPD.
12. The ¹³C NMR chemical shifts of Et₃Si–OH are δ 5.81 and 6.60 ppm (CDCl₃), see: T. Tokuyasu, S. Kunikawa, A. Masuyama and M. Nojima, Org. Lett., 2002, 4, 3595.
13. A. Hosomi, S. Kohara, K. Ogata, T. Yanagi and Y. Tominaga, J. Org. Chem., 1990, 55, 2415.
14. M. Okajima, S. Suga, K. Itami and J.-I. Yoshida, J. Am. Chem. Soc., 2005, 127, 6930.
15. Montmorillonite-catalyzed transformations of large molecules: (a) K. Ebitani, T. Kawabata, K. Nagashima, T. Mizugaki and K. Kaneda, Green Chem., 2000, 2, 157; (b) T. Kawabata, T. Mizugaki, K. Ebitani and K. Kaneda, Tetrahedron Lett., 2001, 42, 8329; (c) T. Kawabata, M. Kato, T. Mizugaki, K. Ebitani and K. Kaneda, Chem. Lett., 2003, 32, 648. Other catalysts: (d) A. Kumar, M. Dixit, S. P. Singh, R. Raghunandan, P. R. Maulik and A. Goel, Tetrahedron Lett., 2009, 50, 4335; (e) S. G. Rha and S.-K. Chang, J. Org. Chem., 1998, 63, 2357.
16. Acetal exchange reactions between cyclic acetals and silyl ethers have been reported: T. Suzuki and T. Oriyama, Synth. Commun., 1999, 29, 1263.
17. K. Motokura, N. Fujita, K. Mori, T. Mizugaki, K. Ebitani and K. Kaneda, Angew. Chem., Int. Ed., 2006, 45, 2605.

---

Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c1cy00040c

---