Preparation of syn-1,2-Diols via Tandem Wittig Rearrangement/Aldol Reaction

Significance

The reaction of an allyl or benzyl glycolate with an aldehyde generated an unexpected product wherein two C-C bonds and two contiguous stereocenters were formed in one step. The [1,2]-Wittig rearrangement occurs under mild conditions and without the use of a strong base. In all cases, syn-1,2-diol products 3 are obtained with the highest diastereoselectivity observed to date for free alcohols. The use of an O-allyl protecting group on 1 is more interesting, as it leaves a synthetic handle in the products for further functionalization (3a-d). The reaction tolerated a wide variety of aldehydes 2, but the migration failed with other O-alkyl groups in 1. For a related 3-component reaction, see: D. A. Nicewicz, J. S. Johnson J. Am. Chem. Soc. 2005, 127, 6170-6171.