Studies related to dihydro-1,4-thiazines. Part I. Rearrangements involving 1,3-sulphur migrations

Abstract

Methyl (3S)-3,4-Dihydro-3-iodomethyl-1,4–2H-thiazine-6-carboxylate (6) undergoes racemisation when heated under reflux in ethyl methyl ketone; deuterium-labelling experiments reveal that a 1,3-sulphur migration is involved. Under corresponding conditions, methyl (3R)-3.4-dihydro-3-iodomethyl-2,2-dimethyl-1,4–2H-thiazine-6-carboxylate (20) rearranges to methyl (3R)-3,4-dihydro-3-isopropenyl-1,4–2H-thiazine-6-carboxylate (8). Methyl (6S)-5,5-dimethyl-4-thia-1-azabicyclo[4,1,0]hept-2-ene-3-carboxylate (21) also affords compound (8) when heated in boiling toluene.