Asymmetric Friedel-Crafts alkylations catalyzed by bis(oxazolinyl)pyridine-scandium(III) triflate complexes.

摘要

I. Asymmetric Catalysis with Bis(oxazolinyl)pyridine Scandium(III) Triflate Complexes Scandium(III) bis(oxazolinyl)pyridine (PyBox) complexes have emerged as general catalysts for a wide range of asymmetric carbon-carbon bond forming transformations in the last six years. This review will present an up to date account on the use of scandium(III) triflate-PyBox complexes in asymmetric catalysis with a focus on proposed stereochemical models when applicable.; II. Enantioselective Friedel-Crafts Reactions of alpha,beta-Unsaturated Acyl Phosphonates Catalyzed by Bis(oxazolinyl)pyridine-Scandium(III) Triflate Complexes. A highly enantioselective Friedel-Crafts alkylation of electron-rich aromatic nucleophiles with alpha,beta-unsaturated acyl phosphonates catalyzed by scandium(III)-PyBox complexes has been accomplished (eq 1). The acyl phosphonate product is efficiently converted to the corresponding ester or morpholine amide by the direct addition of an alcohol (with DBU) or morpholine to the reaction mixture. Stereochemical models based on the crystal structures of the scandium(III)-Inda-PyBox and Ph-PyBox complexes are proposed to account for the reverse stereochemical induction with these catalysts.*; III. Enantioselective Friedel-Crafts Reactions of alpha,beta-Unsaturated 2-Acyl Imidazoles Catalyzed by Bis(oxazolinyl)pyridine-Scandium(III) Triflate Complexes. Highly enantioselective Michael-type indole, pyrrole, and intramolecular Friedel-Crafts reactions with a variety of beta-substituted alpha,beta-unsaturated 2-acyl imidazoles catalyzed by bis(oxazolinyl)pyridine-scandium(III) triflate complexes have been developed (eq 2). The 2-acyl imidazole products were found to be an effective acyl transfer reagent; which esters, amides, ketones, an aldehyde, and a carboxylic acid can be acquired efficiently. Utilization of this methodology, we were able to develop efficient syntheses of a variety of enantiomerically enriched 2-substitued indoles and the alkaloid (+)-heliotridane. In addition, a 7-coordinate pentagonal bipyramidal scandium(III) 1:1:1 product: substrate: catalyst complex is proposed that accounts for the catalyst loading profile and the stereochemical course of the addition reactions.*; *Please refer to dissertation for diagrams.