Synthesis and Reactions of Some 2-Methyl-4-oxo-4 H -1-benzopyrans and 2-Methyl-4-oxo-4 H -1-benzo[ b ]-thiopheno[3,2- b ]pyrans

Abstract

2-Methyl-4-oxo-4 H -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(1 H )-pyridones was achieved under the influence of some carbon nucleophiles (NCCH 2 R). 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.