Annelated furans. XIII. Methylation of 3-Acylbenzofuran-2(3H)-ones

Abstract

Methylation of 3-acylbenzofuran-2(3H)-ones with diazomethane generally led to a mixture of 3-acyl-2-methoxybenzofuran and 3-(α- methoxy)alkylidenebenzofuran-2(3H)-one. These reactions provided the first evidence for the existence of 3-acylbenzo- furan-2(3H)-ones in the 3-acyl-2-hydroxybenzofuran tautomeric form as well as the widely accepted 3-(or-hydroxy)alkylidenebenzofuran-2(3H)one form. In general, methylation of the title compounds with methanol and sulphuric acid gave initially the corresponding 3-(α-methoxy)alkylidenebenzofuran- 2(3H)one while prolonged reaction led to the formation of methyl 2- alkylbenzofuran-3-carboxylates. The mechanism of this acid-catalysed rearrangement and the rearrangement of 3-acetyl-2-methoxybenzo- furan were studied.     The reaction of 3-acetylbenzofuran-2(3H)-one with methyl iodide and potassium carbonate gave a mixture of 3,3-dimethylbenzo-furan-2(3H)-one and 3-methylbenzofuran-2(3H)-one. These products were also obtained by methylating benzofuran-2(3H)-one under similar conditions.