Condensation of N-allylanthranilic acid hydrochloride with potassium thiocyanate furnishes 1-allyl-2- mercapto-4-keto-tetrahydroquinazoline (V). Cyclisation of (V) with HCl provides 2-methyl-9,10-thiopega-10- en-4-one (VII). Bromination of (V) results in its cyclisation to 2-bromomethyl-9,10-thiopega-19-en-4-one, which has been dehydrobrominated to 2-methylene-9,10-thiopega-10-en-4-one (XI). This compound has been converted by bromination and dehydrobromination to 2-bromomethyl-9,10-thiopega-2,10-dien-4-one (XIV). The latter has been condensed with piperidine and with morpholine. The products (XI and XIV) on treat­ment with H2SO4, zinc, and acetic acid furnish 2-methyl-9, 10-thiopega-2,10-mean-4-one (XV). The structures of all these compounds have been confirmed by unambiguous synthesis of (XV). Some of these compounds show weak antibacterial activity.