PALLADIUM-CATALYZED CARBONYL ALLYLATION BY ALLYLIC ALCOHOLS WITH SNCL2

Allylic alcohols can be applied to carbonyl allylation via the formation of pi-allylpalladium complexes, using palladium as catalyst and SnCl2 as a reducing agent. This reaction has chemoselectivity: The reactivity order of allylating agents is allylic carbonate > allylic alcohol > allylic acetate, and that of carbonyl compounds is aldehyde > ketone. High regioselection was observed in polar solvents such as DMF, DMI, and DMSO; carbonyl compounds apparently attacked the more substituted allylic position of pi-allylpalladium complexes to afford only one regioisomer. Diastereocontrol in the carbonyl allylation of aromatic aldehydes by (E)-2-butenol was achieved by the choice of polar solvents; use of DMSO at 25-degrees-C led to syn selection, while anti selection was found at -10-degrees-C in THF. The addition of H2O in any solvent accelerated the carbonyl allylation and enhanced both regioselectivity and the diastereoselectivity. Anti selection in DMF, DMI, and THF-H2O can be explained by the chair form of the six-membered cyclic transition state, while syn selection in DMSO allows us to propose an acyclic antiperiplanar transition state. An NMR spectroscopic investigation demonstrated that the actual allylating agent in dry medium was allyltrichlorotin: H-1, C-13, and Sn-119 NMR spectra of the reaction of allyl alcohol with PdCl2(PhCN)2-SnCl2 in DMF-d7 corresponded to those of the reaction of allyl chloride with PdCl2(PhCN)2-SnCl2 in DMF-d7.