Photochemical transformations. Part 36. Synthesis and photolytic ring contraction of mesoionic 2-alkylthiothiazol-4-ones; a new route to β-lactams
A number of mesoionic 2-alkylthiothiazol-4-ones (6) were prepared by alkylation of rhodanines or by the reaction of α-bromomalonates with dithiocarbamates. The photolysis of these mesoionic compounds proceeds via a highly strained, bicyclic, ling contraction product which rearranges to a thiazolin-2-one (14), loses sulphur, affording a β-aminoacrylate (11), or is trapped by methanol giving methoxy-β-lactams (12) and (13).