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A Highly Tunable Stereoselective Olefination of Semistabilized Triphenylphosphonium Ylides with N -Sulfonyl Imines

2010; American Chemical Society; Volume: 132; Issue: 14 Linguagem: Inglês

10.1021/ja910238f

1943-2984

Dejun Dong, Haihua Li, Shi‐Kai Tian,

Cyclopropane Reaction Mechanisms

The Wittig reaction involving direct olefination of triphenylphosphonium ylides (Ph3P═CHR) with aldehydes is arguably the most often used method for alkene synthesis, but in general it yields mixtures of Z- and E-alkenes for semistabilized triphenylphosphonium ylides (R = aryl or vinyl). We have developed a simple and efficient protocol to improve the stereoselectivity significantly by replacing the aldehydes used in the Wittig reaction with N-sulfonyl imines, which possess distinct electronic and steric properties relative to aldehydes. A broad range of aromatic, α,β-unsaturated, and aliphatic imines bearing appropriate N-sulfonyl groups smoothly undergo olefination reaction with various benzylidenetriphenylphosphoranes or allylidenetriphenylphosphoranes under mild reaction conditions to afford an array of both Z- and E-isomers of conjugated alkenes in good to excellent yields and with greater than 99:1 stereoselectivity. Moreover, this tunable protocol has been successfully applied to the highly stereoselective synthesis of two anticancer agents, DMU-212 and its Z-isomer.