Chemoselective N-Heterocyclic Carbene-Catalyzed Cross-Benzoin Reactions: Importance of the Fused Ring in Triazolium Salts
作者:Steven M. Langdon、Myron M. D. Wilde、Karen Thai、Michel Gravel
DOI:10.1021/ja501772m
日期:2014.5.28
Morpholinone- and piperidinone-derived triazolium salts are shown to catalyze highly chemoselective cross-benzoin reactions between aliphatic and aromatic aldehydes. The reaction scope includes ortho-, meta-, and para-substituted benzaldehyde derivatives with a range of electron-donating and -withdrawing groups as well as branched and unbranched aliphatic aldehydes. Catalytic loadings as low as 5 mol
Catalytic asymmetric synthesis of <i>N</i>-substituted tetrahydroquinoxalines <i>via</i> regioselective Heyns rearrangement and stereoselective transfer hydrogenation in one pot
step-economically obtained in good yield (<97%) and ee (<99%) with readily available substrates. The reaction proceeds through an interesting regioselective Heyns rearrangement/enantioselective transferhydrogenation in one pot. The substrate scope and the reaction mechanism were systematically investigated.
Highly Chemoselective Direct Crossed Aliphatic−Aromatic Acyloin Condensations with Triazolium-Derived Carbene Catalysts
作者:Sarah E. O’Toole、Christopher A. Rose、Sivaji Gundala、Kirsten Zeitler、Stephen J. Connon
DOI:10.1021/jo101791w
日期:2011.1.21
that triazolium precatalysts promote (in the presence of base) highlychemoselectivecrossed acyloin condensation reactions between aliphatic and ortho-substituted aromaticaldehydes. An o-bromine atom can serve as a temporary directing group to ensure high chemoselectivity (regardless of the nature of the other substituents on the aromatic ring) which then can be conveniently removed. The process is