REACTION OF THIANTHRENE CATION RADICAL WITH GRIGNARD REAGENTS; EVIDENCE FOR ELECTRON TRANSFER AND TRAPPING OF ALKYL RADICALS BY THE THIANTHRENE CATION RADICAL

Article abstract of DOI:10.1016/S0040-4020(01)88071-6

Reactions are reported between RMgCl and thianthrene cation radical perchlorate (Th⁺ClO4^-) suspended in ether and tetrahydrofuran (THF).In ether solutions reactions R=Bu, s-Bu, t-Bu, 5-hexenyl, and cyclopentylmethyl.Major products were the alkane, the alkene R(-H) in some cases, and, in the cases of R=Bu, 5-hexenyl, and cyclopentylmethyl, the 5-alkylthianthrenium perchlorate (ThR⁺ClO4^-).When 5-hexenylMgCl was used a mixture of 5-(5-hexenyl)- and 5-(cyclopentylmethyl)thianthrenium perchlorates in the ratio of approximately 2 was obtained.Since the ratio of 5-hexenyl/cyclopentylmethyl in the Grignard reagent was 10.4, it is concluded that the C6 sulfonium ions were formed by radical trapping by Th^.+ after single electron transfer from Grignard to cation radical had occurred, thus allowing for cyclization of 5-hexenyl radical.Formation of ThBu⁺ClO4^- is attributed to the trapping of butyl radical by Th^.+, while formation of RH and R(-H) is in all cases also attributed to alkyl radical reactions.Reactions in THF (R=Me, i-Pr, Bu, s-BU, t-Bu, Ph) led almost exclusively to RH and Th.Polymerization of THF was also initiated and took place slowly giving rise to low molecular weight poly(THF).By using THF-d₈ as solvent for reaction between BuMgCl and Th^.+, it was possible to find Bu groups (¹H-NMR) in the poly(THF-d₈).Polymerization of THF is attributed, in some cases (R=Me, Bu), to alkyl-cation transfer from ThR⁺ to THF.In other cases initiation of polymerization by R⁺ and THF(-H)⁺ is considered.