Novel photochemical rearrangements of dihydro-1,3-thiazines

Abstract

A series of 4-alkyl or 4-phenyl substituted 2,3-dihydro-6H-1,3-thiazine-5-carboxylates are synthesised and photolysed in toluene. The 4-methyl compound rearranges to a thiazolidine, which co-exists as an imino-tautomer 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 derivative gave a skeletally rearranged 2,5-dihydro-6H-1,3-thiazine which slowly rearranged to the corresponding 2,3-dihydro-6H-1,3-thiazine.