CHLOROPEROXIDASE-CATALYZED ASYMMETRIC-SYNTHESIS OF A SERIES OF AROMATIC CYCLIC SULFOXIDES

The chloroperoxidase (CPO) catalyzed oxidation of a series of rigid ar omatic sulfides of well-defined geometry has been studied by the use o f enantioselective gas chromatography for the determination of product composition and sulfoxide enantiomeric excess. The almost planar 1-th iaindane was found to be an excellent substrate, giving a quantitative yield of the (-)-(R)-1-oxide in 99% e.e. The sterically more demandin g next higher homolog with a six-membered heterocyclic ring, 1-thiatet rahydronaphthalene (1-thiochroman), also gave a sulfoxide in high e.e. (greater than or equal to 96%) but in a much lower yield, indicating a preserved stereorecognition ability but a lower turnover rate. A car bonyl group in the 4-position (1-thiochroman-4-one) had no further eff ect on the CPO-mediated sulfoxidation. Enantioselectivity was lost for the symmetric disulfide, 1,3-benzodithiol, indicating an equal access ibility of the Fe=O complex towards both sulfur atoms and an active si te centred above the heme-iron atom. In all cases with pronounced enan tioselectivity the reaction gave the (R)sulfoxide as observed previous ly with alkyl aryl sulfides. A change of oxygen source from hydrogen p eroxide to t-butyl hydroperoxide and a longer reaction time gave a hig her chemical but a lower optical yield, most likely due to an increase d competition by the uncatalyzed oxidation reaction in this case. Copy right (C) 1996 Elsevier Science Ltd