Preparation of various C-2 branched carbohydrates using intramolecular radical reactions

A new and efficient method for the facile synthesis of C-2 branched carbohy drates has been developed using an intramolecular radical cyclization-fragm entation reaction. The desired C-2 branched glucopyranosides were isolated in 40-84% yield. Additionally, an unexpected furanoside was obtained from a tributyltin iodide-promoted rearrangement of the radical intermediate. The C-2 formyl glycal was also isolated in good yield using tris(trimethylsily l)silane (TTMSS) as the reducing agent. This method was extended to synthes ize a beta C-2 branched glucopyranoside, a C-2 branched galactoside and a C -2 cyano glucopyranoside. (C) 2000 Elsevier Science Ltd. All rights reserve d.