Ring-opening of 2,5-diaryl-3-lithiofurans

Abstract

The 2,5-diaryl-3-bromofurans (1) react with butyl-lithium to give the corresponding 2,5-diarylfurans and the allenes (4) or the acetylenes (6); by carrying out the reaction in hexane at 65–70 °C the allenes and acetylenes can be obtained in good yields. Enolate intermediates (5) are proposed; these can also be intercepted by acetic anhydride, to give the acetylenic enol acetates (7), and by aromatic aldehydes, to give the pentenediones (8). 3-Bromo-1-methyl-2,4,5-triphenylpyrrole (2) does not give products of ring-opening with butyl-lithium, but from 4-bromo-2,5-diphenyloxazole (3) an open-chain intermediate (9) is formed which reacts with benzaldehyde to give the amide (10).