Graft polymerization onto a polystyrene resin containing thermolabile azo groups and the effect of the grafted resin on asymmetric reduction of oxime ethers

Abstract

Graft polymerization of various vinyl monomers onto a polystyrene resin (6) containing azo groups having the ability to initiate the radical polymerization was performed. The graft efficiency of vinyl monomers onto 6 increases with time of polymerization and achieves more than 85%. The swelling of 6 affects remarkably the graft efficiency. Scanning electron microscopy (SEM) shows that considerable amounts of graft copolymers are located at the surface of 6. The graft copolymer of chloromethylstyrene onto 6 was treated with (8-( -)-2-amin0-3-@-hydroxyphenyl)-l,l -diphenyl-1 -propano1 to yield a resin (9) carrying chiral amino alcohol functions. Resin 9/borane was used for asymmetric reductions of acetophenone oxime O-methyl and 0-benzyl ethers, leading to 1 -phenylethylamine with 43% and 46% enantiomeric excess (e. e.), respectively. These values are higher than those obtained with the generally used polystyrene resin, suggesting that the enantioselectivity can be improved by modification of the support resin.