Generation and application of organosamariums mediated by samarium diiodide

As new applications of organosamariums, development of SmI2-mediated Barbie r- or Grignard-type reactions, anionic rearrangement and carbenoid generati on are summarized. Reduction of aryl and alkenyl free radicals to the corre sponding organosamariums by SmI2 can be achieved using benzene-HMPA as a so lvent system. Thus, coupling reactions of aryl, alkenyl or alkynyl iodides proceed via organosamarium species in the benzene-HMPA system. alpha-Allylo xy carbanions undergoing [2,3]-Wittig rearrangement are regioselectively ge nerated by an intramolecular 1,5-hydrogen atom transfer of a reactive free radical, a net two-electron reduction of diallyl acetals with the liberatio n of a samarium allyl oxide or a ring opening of oxetanes. [2,3] Rearrangem ent of allylic sulfonium ylides occurs by addition of a samarium carbenoid to allylic sulfides. Reductive dehalogenation of 1,1-dihaloalkenes by SmI2 in benzene-HMPA generates alkylidenecarbenoids, which undergo either 1,5-C- H insertion yielding cyclopentenes or 1,2-shift yielding alkynes.