Alkylation and Oxidation of 6,7-Dihydro-6-methyl-5H-dibenzo[b,g][1,5]thiazocine. Selective Oxidation of the Sulfide Moiety by Transannular Participation of the Amino Group

6,7-Dihydro-6-methyl-5H-dibenzo[b,g][1,5]thiazocine (7) was prepared by cyclization of the corresponding amino alcohol using thionyl chloride in acetonitrile. Methylation of 7 gave N,N-dimethyl derivative (8) as the sole product. Treatment of 7 with various oxidizing reagents, however, afforded the corresponding sulfoxide (9) and/or N-oxide (13), and sulfone (14) depending on the kind of reagent. Oxidation of 7 with sodium periodate furnished N-oxide (13) in 72% yield as a major product along with sulfoxide (9) in 12% yield, while 9 was obtained as a major product (76%) by oxidation with sodium hypochlorite together with a small amount of methoxysulfonium derivative (15) in aqueous methanol. The acceleration in oxidation of 7 compared with diphenyl sulfide as well as production of 15 is ascribed to the transannular participation of the amino group with the chlorosulfonio group or intermediacy of a sulfurane. In addition, structural features of 9 and 15 have been investigated by means of 1H NMR and evidenc...