Chromium(III) tetraphenylporphyrin triflate is an efficient and characteristic Lewis acid catalyst for a regio- and stereoselective rearrangement of epoxides to aldehydes. Optically active β-siloxy aldehydes are easily available through Sharpless epoxidation of allylic alcohols, followed by silylation and rearrangement.
K. Suda, T. Kikkawa, S.-i. Nakajima, T. Takanami, J. Am. Chem. Soc., 2004, 126, 9554-9555.
A tandem Wittig Rearrangement/aldol reaction of O-benzyl or O-allyl glycolate esters generates two carbon-carbon bonds and two contiguous stereocenters with excellent diastereoselectivity in a single step from simple starting materials. The [1,2]-Wittig rearrangement proceeds under very mild reaction conditions.
M. B. Betrand, J. P. Wolfe, Org. Lett., 2006, 8, 4661-4663.