Palladium(II)-Catalyzed Acetalization of Terminal Olefins Bearing Electron-Withdrawing Substituents with Optically Active Diols

Article abstract of DOI:10.1021/jo00385a021

Terminal olefins bearing electron-withdrawing substituents such as CH2=CHCOR (R=Ph, Me, t-Bu), CH2=CHCOOMe, and CH2=CHCN are regioselectively acetalized at the terminal carbon (C1) by diols in the presence of PdCl2 (0.1 equiv) and CuCl (1 equiv) in DME at 50 deg C under an atmosphere of O2 (1 atm).The use of optically active (R,R)-2,4-pentanediol (4) gives homochiral cyclic acetals of aldehyde precursors in good yields.The acetalization of CH2=CHCOR is accompanied by the formation of Michael-type adducts such as 3a (R=Ph).However, of importance is that their formation can be prevented by the use of Na2HPO4 as an additive.Although in an early stage of the reaction of CD2=CHPh with 4, a statistical d scrambling of the starting olefin occurs, no such scrambling is observed with CD2=CHCOPh.Additionally, the acetalization of CD2=CHCOPh with 4 results in 1,2 deuterium migration, together with 25percent d loss.These results are accounted for by the reaction pathways involving oxypalladation, Pd-H elimination, and subsequent ring closure giving enol ether.A catalytic cycle involving the oxygenation of Pd-H species with molecular oxygen is proposed.