A new and flexible route to enantiomerically pure bi- and tricyclic 9-oxabispidines has been developed with use of (1R,5S)-7-methyl-2-oxo-9-oxa-3,7-diazabicyclo[3.3.1]nonane-3-carboxylic acid tert-butyl ester as the common late-stage intermediate. The 9-oxabispidines synthesized were evaluated as the chiral ligands in the Pd(II)-catalyzed oxidative kinetic resolution of secondary alcohols giving good to excellent selectivity factors of up to 19.
Chiral 2-<i>endo</i>-Substituted 9-Oxabispidines: Novel Ligands for Enantioselective Copper(II)-Catalyzed Henry Reactions
作者:Matthias Breuning、David Hein、Melanie Steiner、Viktoriaâ H. Gessner、Carsten Strohmann
DOI:10.1002/chem.200901789
日期:2009.11.23
The CuCl2 complex of the tricyclic 9‐oxabispidine, which carries an 2‐endo,N‐anellated piperidine ring, is an excellent catalyst for enantioselectiveHenryreactions giving the S‐configured β‐nitro alcohols in 91–98 % ee (13 examples). Surprisingly, the analogous copper complexes of the bicyclic 9‐oxabispidines delivered the enantiocomplementary R‐configured products in 33–57 % ee. The respective transition