The reaction of photochemically generated α-hydroxyalkyl radicals with alkynes: a synthetic route to γ-butenolides

The photomediated generation of alpha-hydroxyalkyl radicals from simple acyclic and cyclic alcohols, and acyclic diols, and their Subsequent carbon-carbon bond forming reaction with propiolate esters and acetylenedicarboxylates, gives a mixture of a beta-(hydroxyalkyl)enoate, the result of a formal cis addition. and the unsaturated lactone (gamma-butenolide) resulting from the spontaneous cyclization of the corresponding trans addition product. Treatment of the cis adduct with NBS converts it to the same lactone, and so the method overall constitutes a particularly direct route to this important Structural unit. Cyclic alcohols give rise to spiro-gamma-butenolides. The use of supported photomediators simplifies product isolation and allows for the recovery and reuse of the photomediator. (c) 2008 Elsevier Ltd. All rights reserved.