Synthesis and Reactions of Lactam Sulfonium Salts with a Sulfonio Bridgehead. II. 1, 1a, 4, 5, 6-Pentahydro-6-oxo-2H-thiopyrano[1, 6-d]-4, 1-benzothiazepinium Perchlorates

Abstract

Tricyclic benzothiazepinium salts (5) were prepared by [2⁺ +4] polar cycloaddition of thionium intermediates (4A), generated from corresponding α-chloro sulfides (4) and dienes in the presence of silver perchlorate. X-Ray analysis of 5a revealed that the configuration of the thiazepinone skeleton and the dihydrothiopyran ring is cis-fused.Reactions of benzothiazepinium salts (5) with NaBH₄ or NaH afforded 3, 6-epithiobenzazocinone derivatives (9) in high yields by [2, 3]-sigmatropic rearrangement of an ylide intermediate (11). The stereochemistry of epithiobenzazocinone (9a) was determined by the nuclear Overhauser enhancement (NOE) technique and finally by X-ray analysis of the sulfoxide (10) derived from epithiobenzazocinone (9a) by m-chloroperbenzoic acid (MCPBA) oxidation. Alkylation of epithiobenzazocinone (9a) afforded 3-alkyl-3, 6-epithiobenzazocinones (12) with retention of the configuration at C-3. Dihydrothiopyran derivatives (13) were obtained in good yields by SmI₂ reduction of benzothiazepinium salts (5).