EFFECTS OF SOLVENTS AND ADDITIVES IN THE ASYMMETRIC HECK REACTION OF ALKENYL TRIFLATES - CATALYTIC ASYMMETRIC-SYNTHESIS OF DECALIN DERIVATIVES AND DETERMINATION OF THE ABSOLUTE STEREOCHEMISTRY OF (+)-VERNOLEPIN

Studies on the palladium-catalyzed asymmetric cyclization of alkenyl triflates 3 including the effects of solvents and additives such as alcohol and potassium acetate on the reaction are described. Reaction of 3 in polar solvents such as DMSO, acetonitrile, and NMP gave the cyclized products 2 in low chemical and optical yield while reaction in toluene gave 2 of high enantiomeric excess. Reaction in 1,2-dichloroethane also afforded 2 in excellent optical yield but in very low chemical yield. The chemical yield was greatly improved by the addition of pinacol or potassium acetate to the reaction mixture in 1,2-dichloroethane. Thus the decalin derivatives 2 were obtained in good chemical yield and with excellent asymmetric induction (up to 95% ee). Using derivative 2a as a chiral building block, the first asymmetric synthesis of (+)-vernolepin (9) has been accomplished and its absolute stereochemistry has been determined. Furthermore, we have found through a series of P-31-NMR experiments that the catalytically active LnPd(0) species are readily oxidized to LnPdCl(2) in 1,2-dichloroethane but that the addition of pinacol or potassium acetate prevents this process.