Catalytic tin radical mediated tricyclisations. Part 1. Monocyclisation studies

Abstract

A general strategy for catalytic tin radical mediated, radical cascade reactions is proposed in which three rings are constructed in a single step. The initial step in the tricyclisation process has been examined using 2,3-dideoxy-α-D-erythro-hex-2-enopyranosides bearing unsaturated substituents at the 1-O and/or 4-O-positions. Substrates for cyclisation of substituents at the 1-O-position were prepared by a novel zinc chloride catalysed Ferrier rearrangement of tri-O-acetyl-D-glucal with unsaturated alcohols, whereas substrates for cyclisation of substituents at the 4-O-position were prepared by alkylation or acylation of ethyl 6-O-protected 2,3-dideoxy-α-D-erythro-hex-2-enopyranosides. Propargyl substituents cyclise efficiently, but propenyl substituents less so. Propioloyl substituents undergo hydrostannylation without cyclisation.