Preparation and alkylation of 1,5-dihydro-3H-1,2,4-thiadiazolo[3,4-b]quinazolin-5-one 2,2-dioxides

1,5-Dihydro-3H-1,2,4-thiadiazolo3,4-b]quinazolin-5-one 2,2-dioxides ( 3 ) are prepared by reaction of isatoic anhydrides with methyl N-(chloromethanesulfonyl)carbamimidothioate ( 6 ). The sodium salt of 3a , generated with sodium hydride in N,N-dimethylformamide, is alkylated excusively on N-10. An improved preparation of 6 is described, utilizing a two-phase sulfonylation.