4H,6H-1,3,4Thiadiazino2,3-bquinazolin-6-one with a methyl group in position 3 (6a) has been synthesised by the condensation of 3-amino-2-mercapto-3H-quinazolin-4-one (1) with allyl bromide (2) followed by treatment with bromine and subsequent dehydrohalogenation of the brominated product (4) with ethanolic sodium hydroxide. Its isomeric 3-methyl-2H,6H-1,3,4thiadiazino2,3-bquinazolin-6-one (6b) has also been obtained by condensation of1and bromoacetone (7) followed by cyclisation of the intermediates (8or9) with hydrobromic acid or with concentrated sulphuric acid. The structures have been established on the basis of IR and PMR data.
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