Intramolecular carbolithiation of allyl o-lithioaryl ethers: A new enantioselective synthesis of functionalized 2,3-dihydrobenzofurans

Abstract

A new and easy method for the diastereoselective synthesis of 3-functionalized 2,3-dihydrobenzofuran derivatives from allyl 2-bromoaryl ethers is described. The key step of this transformation involves an intramolecular carbolithiation reaction of allyl 2-lithioaryl ethers. The substituents in both the allyl and the aryl moieties play an important and decisive role in stopping the reaction at the benzofuran thus avoiding a γ-elimination reaction. Finally, this process is amenable to the synthesis of enantiomerically enriched compounds by using ( - )-sparteine as a chiral inductor. © 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.