Dihydropyridones: catalytic asymmetric synthesis, N- to C-sulfonyl transfer, and derivatizations.
ABSTRACT Benzotetramisole (1) promotes the reaction of ammonium enolates derived from arylacetic acids with N-tosyl-α,β-unsaturated ketimines, thus giving dihydropyridones with high diastereo- and enantiocontrol. These products readily undergo N- to C-sulfonyl photoisomerization and are derivatized to afford stereodefined piperidines and tetrahydropyrans.
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ABSTRACT: With the intention of improving synthetic efficiency, organic chemists have turned to bioinspired organocascade or domino processes that generate multiple bonds and stereocentres in a single operation. However, despite the great importance of substituted cyclopentanes, given their prevalence in complex natural products and pharmaceutical agents, the rapid, enantioselective assembly of these carbocycles lags behind cyclohexanes. Here, we describe a Michael-aldol-β-lactonization organocascade process for the synthesis of complex cyclopentanes utilizing chiral α,β-unsaturated acylammonium intermediates, readily generated by activation of commodity unsaturated acid chlorides with chiral isothiourea catalysts. This efficient methodology enables the construction of two C-C bonds, one C-O bond, two rings and up to three contiguous stereogenic centres delivering complex cyclopentanes with high levels of relative and absolute stereocontrol. Our results suggest that α,β-unsaturated acylammonium intermediates have broad utility for the design of organocascade and multicomponent processes, with the latter demonstrated by a Michael-Michael-aldol-β-lactonization.Nature Chemistry 12/2013; 5(12):1049-1057. · 21.76 Impact Factor
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ABSTRACT: An efficient enantioselective approach to form trans lactams and cis lactones in up to 98 % yield with greater than 99 % ee, and greater than 20:1 d.r. using simple aliphatic aldehydes has been developed. The process involves a new pathway to generate enolate intermediates from aliphatic aldehydes by oxidation and deprotonation. NHC=N-heterocyclic carbene, Ts=4-toluenesulfonyl.Angewandte Chemie International Edition 11/2012; · 13.73 Impact Factor