Rearrangements on Acid-Catalyzed Dehydration of Regioisomeric Thiol Adducts Formed from K-Region Arene Oxides

Article abstract of DOI:10.1021/ja00191a027

K-Region 5,6-oxides of chrysene, benzanthracene, and benzophenanthrene undergo nucleophilic trans attack by tert-butylthiolate anion in aqueous dioxane to give mixtures of regioisomeric thiol adducts.These adducts have been separated by HPLC, and the positions of thiol addition have been assigned by NMR and/or CD spectroscopy.Adducts characterized were as follows: from chrysene 5,6-oxide, 5-hydroxy-6-(tert-butylthio) (minor) and 5-(tert-butylthio)-6-hydroxy (major); from benzanthracene 5,6-oxide, 5-(tert-butylthio)-6-hydroxy and 5-hydroxy-6-(tert-butylthio)(equal amounts); and from benzophenanthrene 5,6-oxide, 5-(tert-butylthio)-6-hydroxy (minor) and 5-hydroxy-6-(tert-butylthio) (major).Reaction of either one of a pair of regioisomeric adducts with boron trifluoride in ether gave the same mixture of aryl alkyl thioethers, as a result of sulfur migration, presumably via a common episulfonium ion intermediate.Under these acid conditions, both chrysene adducts gave exclusively 6-(tert-butylthio)chrysene, both benzanthracene adducts gave predominantly (87percent) 5-(tert-butylthio)benzanthracene, and both benzophenanthrene adducts gave predominantly (90percent) 5-(tert-butylthio)benzophenanthrene.We have observed for the first time that thiol adducts of K-region arene oxides also undergo a facile base-catalyzed elimination of water in the presence of sodium methoxide in THF.In contrast to the acid-catalyzed reactions, the reaction of each pure adduct under these basic conditions gave a single aryl alkyl thioether that resulted from dehydration without migration of the sulfur substituent.Because of the dissimilarity in mechanism between the acid and base reactions of the adducts, itis essential that a distinction be drawn between acid- and base-induced dehydrations of K-region thiol adducts, such that the stuctures of the original adducts can only be deduced from the aromatized products of the base-catalyzed dehydration.Reaction of several thiol adducts of benzophenanthrene 5,6-oxide in acid has been observed to yield benzophenanthrene.A proposed sulfenyl chloride intermediate from this reaction in hydrochloric acid has been trapped by its addition to cyclohexene.It is suggested that hydrocarbon formation occurs by attack of a nucleophile on the sulfur of a cationic intermediate.