84194-77-4Relevant articles and documents
A highly enantioselective phosphabicyclooctane catalyst for the kinetic resolution of benzylic alcohols
Vedejs, Edwin,Daugulis, Olafs
, p. 4166 - 4173 (2003)
A new class of chiral phosphines belonging to the P-aryl-2-phosphabicyclo[3.3.0]octane family (PBO) has been prepared by enantioselective synthesis starting from lactate esters and 2,2-dimethylcy-clopentanone enolate 5. A selective enolate alkylation method has been developed for preparation of 9 and 10 using a chelating ester substituent in the triflate alkylating agent 11. Subsequent conversion to the PBO catalysts 2 and 39 relies on a diastereoselective cyclization from the cyclic sulfate 17 and LiPHAr to afford the more hindered endo-aryl phosphines. These phosphines function as efficient catalysts for the kinetic resolutions of aryl alkyl carbinols by benzoylation (16, 21, 22) or iso-butyroylation in the case of the less hindered aryl alkyl carbinol substrates. With o-substituted aryl alkyl carbinols, the enantioselectivities exceed 100, and s = 380 ± 10 has been demonstrated in the case of methyl mesityl carbinol. The PBO- catalyzed acylations probably involve a P-acylphosphonium carboxylate intermediate and a tightly ion paired transition state.
