Syntheses and reactions of 9-substituted 10-phenylthioxanthenium salts: negative evidence for thia-anthracene oligomerisation

Abstract

Various 9-aryl-10-phenylthioxanthenium salts have been prepared and their stereochemistry determined by ¹H n.m.r. spectroscopy. Reactions of the 10-phenylthioxanthenium salts or 10-phenyl-10-thia-anthracenes with aryl-lithiums have been studied in order to investigate whether or not 10-thia-anthracenes cause oligomerisation. The 10-phenylthioxanthenium salts reacted with aryl-lithiums to give 9-phenylthioxanthenes in good yields. However, 10-phenylthioxanthenium salt (19) when treated with phenyl-lithium at –15 to –20 °C gave 9-phenylthioxanthenol (38)(17%) together with 9-phenylthioxanthene (13) because of the lability of 10-phenyl-10-this-anthracene to air. 10-Phenyl-9-(p-tolyl)-10-thia-anthracene (50) generated in situ from the sulphonium salt (22) and lithium di-isopropylamide failed to react with p-tolyl-lithium. An isolable ylide, 9-benzoyl-10-phenyl-10-thia-anthracene (52) was treated with p-tolyl-lithium at 0 °C to give 9-benzoylthioxanthene (4)(82%). In contrast, 9,9,10-triphenylthioxanthenium salt (24) on treatment with phenyl-lithium gave a ring-opened product (40), a ring-contracted product (41), diphenyl sulphide (42), and 9,9-diphenylthioxanthene (12). These results indicate that the 10-phenyl-10-this-anthracenes or the σ-sulphuranes of thioxanthenes do not cause oligomerisation.