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.