Thia-Claisen rearrangements of S-allylic ketene N,S-acetals were carried out using substrates with an external allylic stereogenic centre. High levels of diastereoselectivity were observed only when a bromine substituent was introduced onto the double bond.
Reversal of facial selectivity in a thia-Claisen rearrangement by incorporation of a vinylic bromine substituent
作者:Adam R. Ellwood、Anne J. Price Mortimer、Jonathan M. Goodman、Michael J. Porter
DOI:10.1039/c3ob41580e
日期:——
Thia-Claisen rearrangements have been carried out using N-benzylpyrrolidine-2-thione and chiral allylic bromides derived from D-mannitol. Introduction of a bromine atom onto the double bond of the allylic bromide reverses the sense of diastereoselectivity in the [3,3]-sigmatropic rearrangement. Density functional theory calculations lead us to rationalise the observed selectivity in terms of a Cíeplak