[65415-13-6]  · C11H12OS  · 2-Methoxy-1-phenylthio-1,3-butadiene  · (MW 192.30) (E)

[67315-81-5] (Z)


(Diels-Alder diene3)

Physical Data: bp 85-95 °C/0.005 mmHg.1

Solubility: sol most organic solvents.

Preparative Methods: the pure (Z) reagent is available in two steps from Bis(phenylthio)methane and Acrolein by an Organic Syntheses procedure (eq 1).1 Related dienes may be prepared either similarly or by O-methylation of enolates derived from sulfenylated enones.2

Handling, Storage, and Precautions: the (Z) reagent should be stored in a freezer in the presence of a radical inhibitor to avoid isomerization.1

General Discussion.

2-Alkoxy-1-phenylthio-substituted dienes are highly useful in Diels-Alder reactions due to their ready availability,1,2 good reactivity, high selectivity,3 and the many useful transformations of the product cyclohexenyl sulfides.3,4 As shown in eq 2, the phenylthio group generally controls the regiochemistry. The Lewis acid-catalyzed reactions with enones seem particularly effective.3 Hetero Diels-Alder reactions with diacylimines (eq 3) are also highly regioselective.5 A nice example of the possible product transformations is the conversion in eq 4 with utilization of the Diels-Alder stereochemistry via a 2,3-sigmatropic rearrangement.3

The Diels-Alder reactions of 2-methoxy-1-phenylthiobutadiene with Acrylonitrile (eq 5) served as a key example in arguments supporting a large influence of secondary orbital interactions on the regiochemistry of Diels-Alder reactions, because the regioselectivity is significantly higher for the endo products.6 This argument has been compromised in recent years by a continuing lack of ab initio support for the Woodward-Hoffmann-type secondary orbital interaction.7

Related Reagents.

1-Acetoxy-1,3-butadiene; 2-Methoxy-3-phenylthio-1,3-butadiene; 1-Trimethylsilyloxy-1,3-butadiene; 2-Trimethylsilyloxy-1,3-butadiene.

1. (a) Cohen, T.; Ruffner, R. J.; Shull, D. W.; Fogel, E. R.; Falck, J. R. OS 1980, 59, 202. (b) Cohen, T.; Mura, A. J., Jr.; Shull, D. W.; Fogel, E. R.; Ruffner, R. J.; Falck, J. R. JOC 1976, 41, 3218.
2. Cohen, T.; Kosarych, Z. TL 1980, 21, 3955.
3. Cohen, T.; Kosarych, Z. JOC 1982, 47, 4005.
4. (a) Kozikowski, A. P.; Huie, E.; Springer, J. P. JACS 1982, 104, 2059. (b) Kozikowski, A. P.; Sugiyama, K.; Springer, J. P. JOC 1981, 46, 2426. (c) Evans, D. A.; Bryan, C. A.; Sims, C. L. JACS 1972, 94, 2891.
5. Jung, M. E.; Shishido, K.; Light, L.; Davis, L. TL 1981, 22, 4607.
6. (a) Cohen, T.; Ruffner, R. J.; Shull, D. W.; Daniewski, W. M.; Ottenbrite, R. M.; Alston, P. V. JOC 1978, 43, 4052. (b) Alston, P. V.; Ottenbrite, R. M.; Cohen, T. JOC 1978, 43, 1864. (c) Alston, P. V.; Gordon, M. D.; Ottenbrite, R. M.; Cohen, T. JOC 1983, 48, 5051.
7. Singleton, D. A. JACS 1992, 114, 6563, and references therein.

Daniel A. Singleton

Texas A&M University, College Station, TX, USA

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