Catalytic Enantioselective Pyrrole Alkylations of α,β-Unsaturated 2-Acyl Imidazoles
作者:David A. Evans、Keith R. Fandrick
DOI:10.1021/ol060576e
日期:2006.5.1
[reaction: see text] Enantioselective additions of pyrroles to alpha,beta-unsaturated 2-acyl imidazoles catalyzed by the bis(oxazolinyl)pyridine-scandium(III) triflate complex (1) have been accomplished. The alpha,beta-unsaturated 2-acyl imidazoles were synthesized in high yields through Wittig olefination. A short, enantioselectivesynthesis of the alkaloid (+)-heliotridane has been accomplished utilizing
Enantioselective Addition of Remote Alkyl Radicals to Double Bonds by Photocatalytic Proton-Coupled Electron Transfer (PCET) Deconstruction of Unstrained Cycloalkanols
ring opening of unstrained cycloalkanols by a proton-coupled electrontransfer (PCET) process, to 2-acyl imidazoles previously coordinated to a rhodium-based chiral Lewis acid. High yields and enantioselectivites up to 99% are achieved in 1 h. Mechanistic investigations support the formation of the remote alkyl radical by a PCET process, and theoretical studies explain the observed stereochemistry
Enantioselective Friedel−Crafts Alkylations Catalyzed by Bis(oxazolinyl)pyridine−Scandium(III) Triflate Complexes
作者:David A. Evans、Keith R. Fandrick、Hyun-Ji Song、Karl A. Scheidt、Risheng Xu
DOI:10.1021/ja072976i
日期:2007.8.1
The enantioselective Friedel-Crafts addition of a variety of indoles catalyzed by bis(oxazolinyl)pyridine-scandium(III) triflate complexes (Sc(III)-pybox) was accomplished utilizing a series of beta-substituted alpha,beta-unsaturated phosphonates and alpha,beta-unsaturated 2-acyl imidazoles. The acyl phosphonate products were efficiently transformed into esters and amides, whereas the acyl imidazole adducts were converted to a broader spectrum of functionalities such as esters, amides, carboxylic acids, ketones, and aldehydes. The sense of stereoinduction and level of enantioselectivity were found to be functions of the size of the substrate employed, the substitution on the ligand, and the catalyst loading. Molecular modeling of the catalyst with the bound substrates was performed based on the crystal structures of the catalyst complexes and the sense of stereoinduction observed in the addition reaction. Nonlinear effects over a range of catalyst concentrations implicate a mononuclear complex as the active catalyst.