Kinetically controlled Wittig reactions of ortho-heteroatom substituted benzaldehydes with acetonylides and benzylides give significantly increased proportions of Z-alkenes relative to reactions with benzaldehyde.  Counterintuitively, Z-selectivity is highest where the ylide carbon bears a bulky group. With ethylides, low temperature acid quenching of the Wittig reactions gives increased proportions of erythro-�-hydroxyphosphonium salt, again relative to benzaldehyde.  The harmony of the results across ylide types argues strongly for mechanistic unity as provided in Vedejs's variant of the direct cycloaddition mechanism.

Anomalously high selectivity for <i>cis</i>-oxaphosphetane derived products in the reactions of <i>ortho</i>-heteroatom substituted benzaldehydes with all phosphonium ylide types: Evidence of a unified mechanism for the salt-free Wittig reaction

239th National Meeting (2010)

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Anomalously high selectivity for cis-oxaphosphetane derived products in the reactions of ortho-heteroatom substituted benzaldehydes with all phosphonium ylide types: Evidence of a unified mechanism for the salt-free Wittig reaction