NOVEL PHOTOCHEMICAL REARRANGEMENTS OF DIHYDRO-1,3-THIAZINES

A series of 4-alkyl or 4-phenyl substituted 2,3-dihydro-6H-1,3-thiazin e-5-carboxylates are synthesised and photolysed in toluene. The 4-meth yl compound rearranges to a thiazolidine, which co-exists as an iminot automer in solution. The 4-ethyl derivative gives essentially a single isomer of an acyclic thioamido-diene, whilst the 4-benzyl derivative gives a mixture of all four possible thioamido-dienes. The 4-phenyl de rivative gave a skeletally rearranged 2,5-dihydro-6H-1,3-thiazine whic h slowly rearranged to the corresponding 2,3-dihydro-6H-1,3-thiazine.