SINGLE ELECTRON-TRANSFER MECHANISM IN THE REACTION OF 1,3-DITHIANYLLITHIUM AND ALKYL IODIDES

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(N)2 (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, 6-11% cyclized alkylated product was obtained. This result suggests that when the S(N)2 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 or cyclization 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.