Details associated with the bimolecular 1,4-dipolar cycloaddition reaction of cross-conjugated heteroaromatic betaines

A series of 3,3-disubstituted bicyclic anhydro-4-hydroxy-2-oxo-1,3-thiazinium hydroxides are easily prepared from the reaction of 3H-thiolactams with 1,3-bielectrophiles. These cross-conjugated heteroaromatic betaines undergo regio- and diastereospecific 1,4-dipolar cycloaddition with electron-rich and electron-deficient π-bonds to produce 1,4-cycloadducts containing a carbonyl sulfide bridge. A representative betaine dipole and a...