Synthesis and reactions of some 2-methyl-4-oxo-4H-1-benzopyrans and 2-methyl-4-oxo-4H-1-benzo[b]-thiopheno[3,2-b]pyrans

Abstract

2-Methyl-4-oxo-4H-1-benzothiophenopyran (3) was prepared together with its thio analoge 4. A facial conversion of 3 and some 2-methyl-4-oxo-4 H-1-benzopyrans (5) to 2-oxo-2 H-1-pyrans and 2(1H)-pyridones was achieved under the influence of some carbon nucleophiles (NCCH2R). The behavior of the active methyl group of 3 or 5 toward benzaldehyde, ethyl oxalate, and phthalic anhydride was discussed, where the styryl derivatives 12, 16, the pyruvates 20, 24, and phthalide 33 were obtained, respectively. Bromination of 12, 16, followed by reaction with phenylenediamine and 2-aminothiophenol, led to the formation of quinoxalinyl and benzothiazinyl derivatives. Treatment of the pyruvic acids derived from 20, 24 with phenylenediamine gave quinoxalinyl derivatives, but with benzaldehyde and aniline, atophan analogues were formed. In addition, compound 33 was isomerized to the corresponding phthalone derivative. Compound 3 was allowed to react with amines, hydrazine, hydroxylamine, thiourea, and guanidine, where opening of the pyrone ring was observed and alkylaminobutene, pyrazole, isoxazole, aminopyrimidine, thioxopyrimidine derivatives were obtained, respectively.