Chelation-controlled regioselective endo cleavage and stereoselective C-1 alkylation of pentofuranosides

Abstract

Combinations of Lewis acids and nucleophilic reagents trigger endo-opening of the furanoside ring of methyl furanosides 1, 10 and 13, resulting in the attachment of the nucleophilic group at C-1 of the carbohydrate. The stereoselectivity in the C–C bond-forming step is low for the 2-deoxyfuranosides but very high (dr 1∶99) for the furanosides carrying a methoxy group in the 2-position when a combination of TiCl₄ and Me₂Zn is used. Different selectivities are obtained with Me₂Zn as compared with Me₃Al. Reagents based on several organometallic reagents of Al, Si, Ti and Zn in combination with TiCl₄ can be used.