Development of chiral nucleophilic pyridine catalysts: applications in asymmetric quaternary carbon synthesis.
TADMAP (1a), a new chiral DMAP catalyst, has been designed to place a C(3)-benzylic trityl group over one face of the pyridine ring, while a C(3)-benzylic acetoxy group creates a chirotopic environment on the other face. TADMAP was prepared in four steps (37% overall) from triphenylacetic acid and (dimethylamino)pyridine and was resolved using camphorsulfonic acid. TADMAP catalyzes the enantioselective rearrangement from oxazolyl phenyl carbonates 4 to azlactones 5, from furanyl phenyl carbonate 8 to the furanone 9, from the benzofuranyl carbonates 11a and 11b to benzofuranones 12a and 12b, and from the indolyl carbonates 11c and 11d to oxindoles 12c and 12d. The products are formed in good yield and, in most cases, with practical levels of enantiomer excess at the newly formed quaternary carbon.
Shaw
Scott A
SA
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
Aleman
Pedro
P
Vedejs
Edwin
E