Isothiourea-catalysed transfer hydrogenation of α,β-unsaturated para-nitrophenyl esters

A protocol for the isothiourea-catalysed transfer hydrogenation of alpha,beta-unsaturated para-nitrophenyl esters using Hantzsch ester has been developed. Good to excellent yields are observed using alpha,beta-unsaturated aryl esters bearing electron-withdrawing beta-substituents. The aryl ester products can either be isolated directly in moderate to excellent yields (7 examples, 16-98%) or converted to the corresponding methyl esters (2 examples, 68-70% yield) or benzyl amides (2 examples, 44-88% yield) after in situ reaction of the hydrogenated ester with the appropriate nucleophile. Preliminary experiments showed that modest enantioinduction (76:24 er) is possible when a chiral isothiourea catalyst was used. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

A new protocol has been developed for the isothiourea-catalysed transfer hydrogenation of alpha,beta-unsaturated para-nitrophenyl esters using Hantzsch ester. Good to excellent yields were observed, especially with alpha,beta-unsaturated aryl esters bearing electron-withdrawing beta-substituents. The aryl ester products can be isolated directly in moderate to excellent yields or converted to methyl esters or benzyl amides after in situ reaction with the appropriate nucleophile. Preliminary experiments showed modest enantioinduction when a chiral isothiourea catalyst was used.