ASYMMETRIC AMINOHYDROXYLATION OF SUBSTITUTED STYRENES - APPLICATIONS IN THE SYNTHESIS OF ENANTIOMERICALLY ENRICHED ARYLGLYCINOLS AND A DIAMINE

The catalytic asymmetric aminohydroxylation of a variety of styrene de rivatives and vinyl aromatics using osmium tetroxide in conjunction wi th alkaloid-derived ligands [e.g. (DHQ)(2)PHAL or (DHQD)(2)-PHAL] and haloamine salts of alkyl carbamates (e.g. ethyl carbamate or tert-buty l carbamate) has been investigated. By observing the effect of differe nt aromatic substituents and alkyl carbamates on the regioselectivity, yield and enantioselectivity of the aminohydroxylation reactions, a n umber of conclusions have been reached: (i) the 1-aryl-2-hydroxyethyla mine regioisomers were obtained as the major products in reasonable yi eld and high (greater than or equal to 87%) enantiomeric excess; (ii) tert-butyl carbamate was superior to ethyl carbamate in terms of yield , enantioselectivity and ease of removal of the N-protecting group; (i ii) high (greater than or equal to 96%) enantioselectivity was observe d with a 4-methoxy-substituted styrene whereas ortho-substituted styre nes gave lower enantioselectivities; (iv) chiral ligands (DHQ)(2)PHAL and (DHQD)(2)PHAL gave essentially equal and opposite senses and degre es of asymmetric induction; (v) regioselectivity was ligand dependent with better regioselectivity (and therefore higher isolated yields) ob tained with (DHQ)(2)PHAL than with (DHQD)(2)PHAL. The products of the aminohydroxylation reactions were used to prepare enantiomerically enr iched arylglycinols and a chiral diamine.