Studies related to dihydro-1,4-thiazines. Part V. Intramolecular cyclisations of 3,4-dihydro-3-hydroxymethyl-6-methoxycarbonyl-2H-1,4-thiazines

Abstract

(1R,3R)-3,4-Dihydro-3-hydroxymethyl-6-methoxycarbonyl-2H-1,4-thiazine 1-oxide (5) is converted into methyl (1S,5R)-8-acetyl-2-chloro-7-oxa-3-thia-8-azabicyclo[3.2.1]octane-2-carboxylate (9) by acetyl chloride in acetonitrile. (1S,3R)-3,4-Dihydro-3-hydroxymethyl-4-isopropyl-6-methoxycarbonyl-2H-1,4-thiazine 1-oxide (8) and its (1R)-isomer (7) undergo an analogous reaction,viaa common acetoxysulphonium salt (16), to give methyl (1S,5R)-2-chloro-8-isopropyl-7-oxa-3-thia-8-azabicyclo[3.2.1]octane-2-carboxylate (11). In the presence of acetic acid the last-named derivative is converted into methyl (1S,5R)-2-acetoxy-8-isopropyl-7-oxa-3-thia-8-azabicyclo[3.2.1]octane-2-carboxylate (12), which is identical with the product formed in the reaction of methyl (3R)-3,4-dihydro-3-hydroxymethyl-4-isopropyl-2H-1,4-thiazine-6-carboxylate (25) with lead tetra-acetate.