Regio- and stereocontrolled synthesis and Diels-Alder reactions of (Z)-2-(phenylthio)-1-(trimethylsilyl)-1,3-butadiene

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TetraMdron utters. Vol. 36, No. 48, pp. 8825-8828. 1995 Elsevier SCience LId Printed in Great Britain

Pergamon

0040-4039195 $9.50+0.00

0040-4039(95)01884-0

Regio- and Stereocontrolled Synthesis and Diels-Alder Reactions of (Z)-2-(Phenylthio)-1-(trimethylsilyl)-1,3-butadiene Shang·Shing P. Chou· and Mao·lIsun Chao

Depanment oC Chemistry. Fu Jen Catholic University. Taipei. Taiwan 24205. Republic oC China

ABSTRACT: 1be title compound 4 was synthesized Crom its 3-sulfolcne precursor 3. and the Diels-A1der reactions of 4 were studied.

Diels-Alder reactions are widely used in the synthesis of complex molecules. l Much progress has been made in the preparation of highly functionalized dienes. 2 One important feature of the Diels-Alder reaction which i~ of great interest to both theoretical and synthetic chemists is the regiochemical control of differ~nt groups on competing positions of the diene.3 The introduction of hetero substituents on the diene is especially useful because they would further increase the reactivity of the diene as well as the synthetic versatility of the cycloadducts.4 Since the substituted 1,3-butadienes are often quite sensitive to heat, light and acids, the 3-sulfolenes have been conveniently used as their stable precursors. S We have used this method to synthesize some sulfur-substituted dienes,6 and wish now to report the first synthesis of the title compound which bears both a sulfur and silicon substituent on the diene. Treatment of 3-(phenylthio)-2-sulfolene (1)7 with butyllithium (1 equiv) in THF at -78

oc

followed by the addition of chlorotrimethylsilane (5 equiv) gave 3-(phenyithio)-2-(trimelhylsilyl)• 2-sulfolene (2) in 86% yield. This 2-sulfolene 2 was successfully converted to 3-sulfolene 3 by sequential addition of butyllithium (l equiv) and salicylic acid (1.5 equiv), The 3-sulfolene 3 was desulfonylated by Kugelrohr distillation at 145·150 °C under vacuum (0.1 torr) to give the title compound 4 in 81 % yield.

d

~

S02

1

ci-

SPh

SPh 1.BuLi 2. Me3SiCI

S02

SPh

1. BuLi

siMe 3 2. H+

2

~SiMe3~ 502 3

rC fj ~

SiM~

4

Deprotonation of 2-sulfolt-ne 1 could proceed at C-2 (path 1) or C-4 (path 2).8 To differentiate these two pathways, we carried out the deprotonation of 1 followed by the addition of D20. Only the 8825

8826

2-deuterio-3-(phenyhhio)-2-sulfolene (5) was obtained quantitatively.

This indicates that

deprotonation occurs only at C-2. If the deprotonation had occurred at C-4 and been followed by a deuteration at C-2, then the equilibration to the 3-sulfolene would have resulted in the Connation of dideuterated product 6 which was clearly ruled out by the IH NMR and MS spectra.

Q

SPh + Bull

path 1

fp~h2

[d-S~]

Go

5Ph

DozO

502

502

5

-0 - [d:"] SPh

50 2

02

O~

[BS]

o

lj-o

5Ph

base

6

We have attempted to generate the diene 4 directly by heating 2-sulfolene 2 with DBU in the hope that the base would isomerize 2 to 3 which could then undergo desulfonylation. 9 Unfortunately, the trimethylsilyl group was lost during such an operation. This is quite understandable, because the allylic silane intermediate would not be stable under basic thermolysis. To circumvent this problem, we isolated the 3-sulfolene 3 and then carried out the desulfonylation under neutral conditions. Deprotonation of 2 with butyllithium occurred only at C-4 to generate an anion which could be reprotonated at C·2 to give the desired 3-sulfolene 3 or at C-4 to give the starting material 2. It was found that the proton source and the quench temperature used were very important in determining the amount of these twO isomers. The most favorable condition we found for obtaining 3 was to add salicylic acid (which was readily soluble in THF) at -120 0C leading to the isolation of 2 (51 %) and 3 (38%). If the quench temperature was above -90 oC, only 2 was obtained. These two products were easily separated by flash column chromatography, and 2 could be recycled to 3.

C"J-

5Ph

S02

2

SiMe3 -

Bull

[5Ph -4 SiM83-

-~ ~O?-

-

5Ph

d-5iMe3 50 2

5Ph

]

W

-

O502

3

SiMe3

8827

Kugelrohr distillation of 3-sulfolene 3 gave the desired diene 4 in 81 % yield. The stereochemistry of 4 was found to be Z by the NOB technique of proton NMR spectroscopy. The Diels-Alder reactions of 4 were also investigated. Heating the diene 4 with N-phenylmaleimide in toluene at 80 0C gave the cycloaddition product 7 in 88% yield. The stereochemistry of 7 was elucidated by proton decoupling and NOB experiments. Thus, the cycloaddition proceeds with endo selectivity, indicating that the secondary orbital effect is more important than the steric effect of the trimethylsilyl group in determining the stereoselectivity of the Diels-Alder reaction of 4.

0=\)=0

:l"=\

iMe 3

~h toluene, 80 0 C, 10h

4 7(88%)

The cycloaddition of 4 with methyl propynoate could in principle give two regioisomers. To simplify the structural identification, the cycloaddition products were directly treated with DDQ to yield the aromatic products 8 and 9. The structure of product 8 was identified by spectroscopic methods. Since no regioisomer of 8 was obtained, this shows that the regiochemistry of the Diels-Alder reaction of diene 4 is determined by the phenylthio group. This regioselectivity is much better than that of 2_(phenylthio)-3-(trimethylsilyl)-1,3-butadiene, which shows an 85: 15 regiocontrol favoring the phenylthio group.I 0 The product 9 was identical with that reported in the literature,l1 and was apparently obtained by cleavage of the trimethylsilyl group before aromatization.

HC=CCC>.!Me

(5 eq)

000 (1 eq)

sealed tube, 80 0 e, 82h 4

SPh

MeO

-P-~Me3

+

M.ofPh

0 8(38%)

9 (16%)

8828

Acknowledgment: Financial support from the National Science Council of the Republic of China (NSC 84-2113·M-03~3)is gratefully acknowledged. References: 1.

Carruthers, W. Cyc/oaddition Reactions in Organic Synthesis, Pergamon: Oxford, 1990.

2. 3.

Fringuelli, F.; Tatichi, A. Dienes in the Diels-Alder Reaction, Wiley: New Yorlc, 1990. (a) Houk, K N. Ace. Chem. Res. 1975,8, 361. (b) Alston, P. V.; Ottenbrite, R. M.; Guner, O. F.; Shillady, D. D. Tetrahedron 1986,42,4403. (c) Pegram, J. J.; Anderson, C. B. Tetrahedron Lett. 1991,32, 2197. (d) Kosugi, H.; Hoshino, K.; Uda, H. J. Chem.

Soc., Chem. Commun. 1992, 560. (e) Chou, T. S.; Chang, C. Y.; Wu, M. C.; Hung, W. H.; Liu, H. M.; Yeh, W. Y. J. Chem. Soc., Chem. Commun. 1992, 1643. (0 Chou, S. S. P.; Cheng, M. C. J. Org. Chem. 1993,58,967.

4.

Petrzilka, M.; Grayson, J. T. Synthesis 1981, 753.

5.

(a) Chou, T. S.; Tso, H. H. Organic Prep. Proc.lnt.1989, 21, 259. (b) Chou, T. S.; Chou, S. S. P. J. Chin. Chem. Soc. 1992,39, 625. (c) Ando, K; Kanake, M.; Suzuki, T.; Takayama, II. Tetrahedron 1995,51, 129 and references cited therein.

6.

(a) Chou, S. S. P.; Liou, S. Y.; Tsai, C. Y.; Wang, A. J. J. Org. Chem. 1987,52, 4468. (b) Chou, S. S. P.; Sun, D. 1.; Wey, S. J. Synth. Commun. 1989,19, 1593. (c) Chou, S. S.P.; Sun, C. M. Tetrahedron Lett. 1990,31, 1035. (d) Chou, S. S. P.; Wey, S. J. J. Org.

Chem. 1990,55, 1270. (e) Chou, S. S. P.; Lee, W. H. Synthesis 1990, 219. (0 Chou, S. S. P.; Yuan, T. M. Synthesis 1991, 171. (g) Chou, S. S. P.; Tsao, H. J.; Lee, C. M.; Sun, C. M. J. Chin. Chem. Soc. 1993,40, 53. (h) Chou, S. S. P.; Lee, C. S.; Cheng, M. C.; Tai, II. P. J. Org. Chem.1994,59, 2010. 7.

Chou, S. S. P.; Sun, D. 1.; Tai, H. P. J. Chin. Chem. Soc. in press.

8.

(a) Chou, T. S.; Yu, C. F. J. Chin. Chem. Soc. 1987,34, 211. (b) Broaddus, C. D. Ace.

9.

Chem. Res. 1969, 1, 231. (a) Mock, W. L. J. Am. Chem. Soc. 1966,88,2857. (b) McGregor, S. D.; Lemal, D. M. J. Am. Chem. Soc. 1966,88, 2858. (c) Mock, W. L. J. Am. Chem. Soc. 1975,97, 3666.

10. 11.

Manly, D. G.; Amstutz, E. D. J. Org. Chem. 1957,22,323. Chou, S. S. P.; Tsai, C. Y.; Sun, C. M. J. Chin. Chem. Soc. 1989,36, 227.

(Received in Japan 8 August 1995; revised 28 September 1995; accepted 6 October 1995)