Use of chiral B(III) complexes in the cycloaddition of C,N-diphenylnitrone to tert-butyl vinyl ether
作者:Pau Bayón、Pedro de March、Marta Figueredo、Josep Font、Jordi Medrano
DOI:10.1016/s0957-4166(00)00405-5
日期:2000.11
The 1,3-dipolar cycloaddition of C,N-diphenylnitrone to tert-butyl vinyl ether in the presence of several chiral B(III) complexes which incorporate different bidentate ligands has been investigated. The use of these B(III) species reverses the endo/exo diastereoselectivity in relation to the uncatalysed reaction, giving trans cycloadducts as major products. Some of the catalysts gave very fast and high yielding reactions, but the enantioselectivities were only low to moderate. (C) 2000 Elsevier Science Ltd. All rights reserved.
Solution and Solid-State Studies of a Chiral Zinc-Sulfonamide Complex Relevant to Enantioselective Cyclopropanations
作者:Scott E. Denmark、Stephen P. O'Connor、Scott R. Wilson
A highly distorted tetrahedron formed by the four nitrogen atoms around zinc in the crystalline zinc-sulfonamide complex 1 may explain its catalytic activity in asymmetric cyclopropanations. The agent is formed by deprotonation of (R,R)-N,N'-cyclohexane-1,2-diyl)bis(n-butanesulfonamide) with diethylzinc and addition of 2,2'-bipyridyl.