Single Electron Transfer Mechanism in the Reaction of 1,3-Dithianyllithium and Alkyl Iodides

Article abstract of DOI:10.1021/jo00004a051

The reaction between 2-lithio-1,3-dithiane and optically active (R)-2-iodooctane was found to proceed with complete inversion of configuration.This result suggests that the S_N2 (rather than single electron transfer (SET)) mechanism is the preferred pathway for reaction between dithianyllithium and unhindered alkyl halides.When the neopentyl-type radical probe 5,5-dimethyl-6-iodo-1-hexene was used as the substrate halide, 6-11percent cyclized alkylated product was obtained.This result suggests that when the S_N2 pathway is blocked, SET mechanisms become operative to some extent, at least with iodide as the halogen.The reaction of dithianyllithium and (R)-2-iodooctane and 5,5-dimethyl-6-iodo-1-hexene, with hexane as the solvent, proceeds under heterogeneous conditions to bring about complete racemization of the respective iodide.These results demonstrate for the first time that 2-lithio-1,3-dithiane can act as electron donor in reactions initiated by electron transfer to alkyl iodides.