Isoquinoline- and piperazinedione-derived α-acylamino peroxide moieties in asymmetric oxidation of sulphides and epoxidation of naphthoquinones

Abstract

The application of chiral α-acylamino hydroperoxide moieties in asymmetric sulphoxidation and epoxidations was pursued. In order to synthesize new isoquinoline-derived α-acylamino hydroperoxides isoquinolines were treated with (R)-menthyl chloroformate and hydrogen peroxide. Instead of the expected hydroperoxides novel bis(2-menthyloxycarbonyl-1,2dihydroisoquinolin-1-yl) peroxides were obtained as 1:1 epimeric mixtures by a subsequent reaction. 1:1 mixtures of t-butyl (2-menthyloxycarbonyl-1,2-dihydroisoquinolin-1-yl) peroxides were formed from t-butyl hydroperoxide, isoquinoline and (R)-menthyl chloroformate. For eventual in situ preparation of chiral (R)-menthyloxycarbonyl-1,2-dihydroisoquinolin-1-yl) hydroperoxides and their application in stereoselective O-transfer reactions, isoquinolines were combined with (R)-menthyl chloroformate, hydrogen peroxide and metal alkoxides. These mixtures allowed a stereoselective synthesis of aryl methyl sulphoxides from corresponding sulphides. The stereoselectivity results from a kinetic resolution of racemic sulphoxides formed in the first step wherein the (S)-enantiomer was faster oxidized to the corresponding sulphone. As another type of chiral α-acylamino hydroperoxide moiety piperazinedione hydroperoxide was applied in the transformation of aryl methyl sulphides into sulphoxides. Low enantioselectivities were achieved. The same reagent allowed a high yielding epoxidation of naphthoquinones, but again in modest stereoselectivities.