[4 + 2]-Cycloadditionen von α, β- ungesättigten hydrazonen. Teil3. Isothiazolo[4,5-b]pyridin-3(2H)-on-1,1-dioxide (= 4-azasaccharine)

4 + 2] Cycloaddition of α, β-Unsaturated Hydrazones: Isothlazolo4,5-b]pyridin-3(2H)-on 1,1-Dioxides (= 4-Azasaccharine Derivatives) The 4 + 2] cycloaddition of α, β -unsaturated hydrazones of type 1 (1-azabuta-1,3-dienes) with isothiazol-3(2H)-on 1,1-dioxide derivatives 10 affords, depending on the solvent used, picolinamides 15 or 17 , 4,7-dihydro-4-azasaccharine 14 or 4-azasaccharine derivatives 16 (Scheme 4). The course of the reaction is mainly influenced by the substituent R of the dienophile 10 .