Generation and reactions of samarium carbanions mediated by samarium iodide

Reduction of aryl and vinyl radicals to the corresponding organosamarium species by SmI2 can be attained by using benzene-HMPA as a solvent system. Thus, SmI2-mediated Barbier- and Grignard type coupling reactions between ketones and aryl, vinyl, or alkynyl iodides proceed via organosamarium species in benzene-HMPA. Reductive dehalogenation of 1,1-dihaloalkenes by SmI2 in benzene-HMPA generates alkylidenecarbenes, which undergo either 1,5-C-H insertion giving cyclopentens or 1,2-shift giving alkynes. On the other hand, SmI2 was found to be useful to effect 2,3-rearrangement under mild conditions. Metalated ethers undergoing Wittig rearrangement are regioselectively generated by either an intramolecular 1,5-hydrogen transfer of a vinyl radical, generated by a single electron transfer from SmI2 to gamma-haloallyl ethers, or a net two-electron reduction of diallyl acetals with the liberation of an allyloxy samarium by SmI2 in acetonitrile. 2,3-Rearrangement of allylic sulfonium ylides can be effected by the reaction of allylic sulfides with samarium carbenoid, generated from CH2I2 and SmI2 in THF.