Titanium mediated asymmetric aldol reaction with α-fluoropropionimide enolates

Aldol reaction utilising Evans N-(alpha-fluoropropyl)-2-oxazolidinones with TiCl4 have been explored. Reactions of N-(alpha-fluoropropyl)-2-oxazolidinones with aliphatic aldehydes generated (x-fluoro-p-hydroxy-aldol products with high diastereoselectivities. When (alpha R)- and (alpha S)-N-(alpha-fluoropropyl)-2-(4S)-oxazolidinones were explored as substrates they gave rise to identical aldol diastereoisomer products. Examination of the enolates formed in each case by F-19 NMR, after treatment with TiCl4, indicated that both preparations gave the same predominant enolate. This was assumed to be the E-enolate. The alpha-fluoro-beta-hydroxy-aldol products were removed from the auxiliary either by alcoholysis or reduction and converted to the corresponding alpha,beta-difluoro products by treatment with Deoxofluor (TM) (C) 2007 Elsevier B.V. All rights reserved.