Reactions of Phenylmagnesium Chloride and Phenyllithium with Thianthrene Cation Radical Perchlorate. Evidence for Electron Transfer: Formation and Decomposition of 5-Substituted Thianthreniumyl Perchlorates

Article abstract of DOI:10.1021/jo00268a024

Reaction of thianthrene cation radical perchlorate (Th<*>⁺ClO4^-), suspended in either ether or THF, with PhMgCl, and reaction of Th<*>⁺ClO4^-, suspended in ether, with PhLi in C6H12/ether, gave largely benzene and Th. 5-Phenylthianthreniumyl perchlorate (1a) was formed in the Grignard reactions but was not obtained in the PhLi reaction.Diphenyl sulfide (Ph2S) and dibenzothiophene (DBT) were obtained with PhMgCl and PhLi in ether, but not with PhMgCl in THF.Small amounts of ethyl 1-phenylethyl ether and 2-phenylethyltetrahydrofuran (PhTHF) were also formed.Reaction with PhMgCl in THF-d8 and with PhLi in (C2D5)2O gave a mixture of C6H6 and C6H5D.These results show that phenyl radical (Ph<*>) was formed in the cation radical reactions and abstracted H(D) atom from the solvent.The results suggest also that Ph<*> was trapped by Th<*>⁺, leading to 1a.However as shown with control reactions, 1a reacted further with PhMgCl (slowly) and PhLi (rapidly) and was converted into Ph2S and DBT.Control reaction of PhLi with 1a gave Ph2S and DBT in high, approximately equal yields.Reaction with 5-(p-tolyl)thianthreniumyl perchlorate (1b) analogously gave phenyl p-tolyl sulfide and DBT.Reaction of PhMgCl with 1a was slow and incomplete and gave not only Ph2S and DBT but also some 2-phenyl-2'-(phenylthio)diphenyl sulfide (2a) and a mixture of 1- and 2-phenylthianthrene (together designated as 3a).An analogous reaction occured between PhMgCl and 1b.Reaction of 1a with BuMgCl gave BuSPh and DBT, some 2-(phenylthio)diphenyl sulfide (4), and some 2-(butylthio)-2'-phenyldiphenyl sulfide (5a).In contrast, reaction of PhMgCl with 5-butylthianthreniumyl perchlorate (1e) gave mainly benzene and Th, while reaction of BuMgCl with 1e gave mainly butane, octane, and Th analog with a small amount of 2-butyl-2'-(butylthio)diphenyl sulfide (5e).Reaction of PhLi with 1e and its analogues 5-methyl- and 5-ethylthianthreniumyl perchlorate (1c and 1d, respectively) gave benzene, Th, the corresponding alkyl phenyl sulfide and DBT, and small amounts of 2-(alkylthio)-2'-phenyldiphenyl sulfide (2c-e).Formation of benzene in these reactions is attributed to deprotonation of the alkyl group in 1c-e and concomitant formation of an ylide (6-8).Ylide 6, from reaction of PhLi with 1c, was trapped by reactions with subsequently added water and phenol (reconverting 6 to 1c) and with added benzophenone, leading to Th and 1,1-diphenyloxirane (9).Diphenylmercury did not react with 1a in acetonitrile solution.The apparent complexity of reactions of Th<*>⁺ClO4^- with PhMgCl and PhLi is better understood in the light of knowledge about reactions of 1a-e.The comparative simplicity of reaction of Th<*>⁺ClO^-, with Ph2Hg is also made clearer.