Studies in [3.3] sigmatropic rearrangement: regioselective synthesis of 1-aryloxymethylpyrano[2,3-c][1]benzopyran-5(3H)-one and 1-aryloxymethyl-2-methylfuro[2,3-c][1]benzopyran-4-one

Abstract

3-(4-Aryloxybut-2-ynyloxy)[1]benzopyran-2-one (1) in refluxing chlorobenzene gave exclusively 1-aryloxymethylpyrano[2,3-c][1]benzopyran-5(3H)-one (6) by a pericyclic path. Compound (1) when heated in nonpolar solvents or in the presence of acid or base, gave exclusively 1-aryloxymethyl-2-methylfuro[2,3-c][1]benzopyran-4-one (10). Additionally this reaction has been studied in the presence of a radical initiator, viz., azoisobutyronitrile (AIBN), and induced to follow mainly the radical pathway to give the products (10). All the butynes (1) studied so far underwent sigmatropic rearrangements at the 4-coumarin-3-yloxypropynyl function of compound (1) to give product(s)(6) and/or (10).