Ring‐opening reactions of 5‐(aryl)thianthrenium bromides with aryl thiolates

A series of 5‐(aryl)thianthrenium bromides ( 6a–e ) with aryl (Ar) groups phenyl ( a ), p ‐tolyl ( b ), p ‐anisyl ( c ), p ‐chlorophenyl ( d ) and p ‐bromophenyl ( e ) was prepared by reaction of thianthrene 5‐oxide with the appropriate Grignard reagent ArMgBr. Reactions of 6a–e with aryl thiolates (Ar′SNa, Ar′ = phenyl, p ‐tolyl and p ‐chlorophenyl, 7a–c ) were carried out in MeCN at room temperature. Products from 6a–c were a small amount of arene [benzene ( 8a ) and toluene ( 8b )], and substantial amounts of ArSAr′ ( 9 ), thianthrene (Th) and a trisulfide, namely a 2‐(ArS)‐2′‐(Ar′S)‐diphenyl sulfide ( 10 ). Products from reactions of 6d,e were smaller amounts of 9 and 10 but substantial amounts of 1,4‐di(Ar′S)benzene ( 11 ) and a tetrasulfide ( 12a–c ). The reactions that lead to products 9 – 12 are attributed to ligand coupling (LC) pathways in sulfuranes formed by attack of Ar′S − at the sulfonium S atom of 6 . In the formation of 11 and 12 the halogen atom (Cl, Br) is first displaced from 6d,e by Ar′S − , giving a new thianthrenium ion ( 14 ) from which sulfurane formation ( 15 ) follows. Products 10 and 12 result from opening of the thianthrenium ring of sulfuranes 13 and 15 through LC. Products were assayed with a combination of GC and isolation with TLC, and were identified with a combination of GC (authentic compounds), x‐ray crystallography ( 10a ), elemental analyses and high‐resolution mass spectrometry. The reactions of 6 are compared with earlier reactions of 5‐(alkoxy)‐and 5‐(alkyl)thianthrenium salts ( 1 and 2 ). Copyright © 2002 John Wiley & Sons, Ltd.