Influence of Lewis Acids on the Diels–Alder Reaction. IV. Reaction of 2-Methyl- and 2-Phenylfuran with Ethyl Propiolate

The AlCl 3 -promoted reactions of 2-methyl- and of 2-phenylfuran with ethyl propiolate afford as major products ethyl 5-hydroxy-2-methyl- and 2-phenylbenzoates (6a, 6b). Also isolated as minor by-products of these reactions are ethyl 3-(2-furyl-5-methyl)acrylate (5a), ethyl 3-(2-furyl-5-phenyl)acrylate (5b), ethyl 3,3-di(2-furyl-5-methyl)propionate (10a), ethyl 3,3-di(2-furyl-5-phenyl)propionate (10b), and ethyl 2-hydroxy-5-methylbenzoate (8a).