Hetero-Diels-Alder Reaction of some 1,3-Diaza-1,3-butadienes with Ketenes. Synthesis of Functionalized Pyrimido[1,2-b]-benzothiazoles and 1,3,4-Thiadiazolo-[3,2-a] pyrimidines

Article abstract of DOI:10.1007/BF00807795

Reaction of 1,3-diaza-1,3-butadienes (1a-c) with various ketenes and chloroketenes results in the formation of substituted 4-oxo-pyrimido[2,1-b]benzothiazoles(4a-d) and 1,3,4-thiadiazolo[3,2-a]pyrimido-4-ones (4e,f). Reaction of 1,3-diaza-1,3-butadienes 1d,e with ketenes and chloroketenes leads to the 2-morpholine-substituted compounds 7 and 15, respectively. All reactions proceed via formation of [4 + 2] cycloadducts that eliminate methylthiol, methylsulfenyl chloride, or morpholine.