Apparent Charge Reversal of π-Allylpalladium Complex : Application to Carbonyl Allylation by Allylic Alcohols

Palladium-catalyzed carbonyl allylation by allylic alcohols with SnCl2 smoothly proceeds in aqueous medium under air. The actual allylating agent in the carbonyl allylation by allyl alcohol in dry medium is allyltrichlorotin, which is prepared via (1) oxidative addition of allyl alcohol to Pd (0) complex with SnCl2, (2) insertion of SnCl2 to π-allylpalladium complex, followed by (3) reductive elimination of π-allylpalladium trichlorostannate. Allylic alcohols, preparing π-allylpalladium complexes, function as synthons of allylic carbanions. In other words, this implies the apparent charge reversal of electrophilic π-allylpalladium complexes. The carbonyl allylation by allylic alcohols can achieve high chemo-, regio-, and diastereoselection by the choice of solvent, and can be applied to chelation-controlled diastereoselection in polar solvents.