RATE ENHANCING EFFECT OF HYDROGEN-CHLORIDE AND METHANESULFONIC-ACID ON THE INTRAMOLECULAR ASYMMETRIC REDUCTION OF O-AMINOACETOPHENONE AND O-BENZOPHENONE WITH DIISOPINOCAMPHEYLBORANE

While o-hydroxyaceto- and -benzophenones undergo reduction with B-chlo rodiisopinocampheylborane (1) and diisopinocampheylborane (2) at the s ame rate, the reduction of o-carboxyaceto- and -benzophenones is faste r with 2 as compared with 1. The rate retardation for the reaction of keto acids with 1 was accounted by a competition between an intra- and intermolecular reduction. In contrast, o-aminoaceto- and -benzophenon e undergo faster reduction with 1 than with 2. The rate enhancing infl uence of HCl and MeSO(3)H on the intramolecular asymmetric reduction o f these amino ketones with 2 has been tested and confirmed. (C) 1997, Elsevier Science Ltd.