Rh(II) catalyzed oxonium ylide generation of trans-3-styryltetrahydropyranone-5-diazoacetoacetates 1  and their subsequent rearrangements unexpectedly form two diastereoisomers through both the [1,2]-Stevens and [2,3]-sigmatropic processes. The distribution of diastereoisomeric products is independent of substituents and of dirhodium catalyst.  The formation of a second diastereoisomer for the symmetry-allowed concerted [2,3]-sigmatropic rearrangement process supports the hypothesis that the presence of two conformational isomers for diazoacetoacetate 1  lead to the formation of two non-interconvertable oxonium ylide diastereoisomers. 

Mechanism of the [1,2]-Stevens and [2,3]-sigmatropic rearrangements in the generation and reactions of oxonium ylides

243rd National Meeting (2012)

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