Peterson alkenation stereochemistry

The use of sulfur in the Peterson reaction can be extended to the optically pure lithio anion of S phe-nyl-S-(trimethylsilyl)tnethylW-tosylsulfoxiniine (330 equation 76). Unlike most Peterson alkenations t reaction is selective for the formation of the ( )-alkene isomer (331) with aldehydes. In addition, the stereochemistry of the sulfoximine is maintained. 

As a consequence of the presumed irreversibility of die first step of the Peterson reaction, the stereochemistry of the elimination was determined solely by the relative rates (ki and ki ) of formation of threo- and erythro- -sHyl alkoxides (141) and (142), as indicated in Scheme 66. Support for the irreversibility of this step comes from the experiments on the nucleoidiilic opening of the diastereomeric epoxides (143) and (144). Thus, the syn- and onri-epoxides, when treated widi lithium dipropyl cuprate, yielded the threo- and erythro- -sHy alcohols (145) and (146), respectively. Treatment of die threo isomer with base gave the (Z)- ene exclusively and the erythro isomer gave the ( )-alkene. The high levels of selectivity for this elimination indicated diat die initial addition is not revenible. The elimina-... 

The Peterson olefination is a two-step process for the formation of alkenes from an a-silylcarbanion and an aldehyde or ketone. The first step is an addition reaction that affords both syn and anti p-hydroxysilanes. The stereochemistry is then controlled during the elimination step by using either an acid or a base. Reviews Kano, N. Kawashima, T. In Modem Carbonyl Olefination-Methods and Applications Takeda, T. Ed. Wiley-VCH Weinheim, 2004 Chapter 2 The Peterson and Related Reactions, pp. 18-103. (b) Kelly, S. E. In Comprehensive Organic Synthesis Trost, B. M. Fleming, 1., Eds. Pergamon Oxford, 1991 Vol. 1, Chapter 3.1 Alkene Synthesis, pp. 731-737. (c) Ager, D. J. Org. React. 1990, 38, 1-223. (d) Ager, D. J. Synthesis 1984, 384-398. 

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