Abstract
AbstractA new general concept for α,β‐unsaturated acyl ammonium catalysis is reported that uses p‐nitrophenoxide release from an α,β‐unsaturated p‐nitrophenyl ester substrate to facilitate catalyst turnover. This method was used for the enantioselective isothiourea‐catalyzed Michael addition of nitroalkanes to α,β‐unsaturated p‐nitrophenyl esters in generally good yield and with excellent enantioselectivity (27 examples, up to 79 % yield, 99:1 er). Mechanistic studies identified rapid and reversible catalyst acylation by the α,β‐unsaturated p‐nitrophenyl ester, and a recently reported variable‐time normalization kinetic analysis method was used to delineate the complex reaction kinetics.
Highlights
A new general concept for a,b-unsaturated acyl ammonium catalysis is reported that uses p-nitrophenoxide release from an a,b-unsaturated p-nitrophenyl ester substrate to facilitate catalyst turnover
Lewis base organocatalysis is a widely studied field due to the diverse range of molecular frameworks that can be produced with high levels of regio, chemo- and stereocontrol.[1]
At the carboxylic acid oxidation level a variety of ammonium intermediates with differing reactivity can be accessed from readily available substrates using tertiary amine Lewis bases (Scheme 1 a)
Summary
A new general concept for a,b-unsaturated acyl ammonium catalysis is reported that uses p-nitrophenoxide release from an a,b-unsaturated p-nitrophenyl ester substrate to facilitate catalyst turnover. Given the moderate isolated yields of PNP ester products, the addition of a suitable nucleophile at the end of the reaction was used to give a range of readily isolable
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