Base-catalysed intramolecular cycloadditions of allyl 3-phenylprop-2-ynyl ethers and 4-methylpent-4-en-2-ynyl prop-2-ynyl ethers

Abstract

The base-catalysed intramolecular cycloadditions of allyl 3-phenylprop-2-ynyl ethers (VIa and b) leading to tetrahydronaphtho[2,3-c]furans [(X) and (XI)] is rationalised in terms of (a) a base-catalysed isomerisation of the acetylenic group to an allene, (b)[_π4 +_π2] cycloaddition of the allyl group to the phenylallene, and (c) hydrogen shifts (Scheme 2). The base-catalysed intramolecular cycloaddition of 4-methylpent-4-en-2-ynyl prop-2-ynyl ether (VIIa) proceeds in an analogous manner via either mono- or bis-allenic intermediates (Scheme 3).