N-heterocyclic carbene (NHC) organocatalysis is widely employed for the umpolung of aldehydes and recently to the umpolung of Michael acceptors and aldimines. Described herein is the NHC-organocatalyzed umpolung of aldimines for the enantioselective synthesis of nitrogen heterocycles. The bisimines generated from the condensation of 1,2-phenylenediamines and salicylaldehydes undergo intramolecular cyclization in the presence of a chiral NHC catalyst, resulting in the formation of dihydroquinoxalines in moderate to good yields and er values. Detailed DFT studies shed light on the role of −OH groups in stabilizing the initially generated aza-Breslow intermediates via intramolecular hydrogen bonds. Preliminary photophysical studies on the synthesized dihydroquinoxalines revealed that these molecules can be used for the sensing of various acids and bases.

Chiral NHC-catalyzed kinetic resolution of N-aryl aminomaleimides allowing the synthesis of C–N axially chiral N-aryl aminomaleimides via remote chirality control is presented. The catalytically generated α,β-unsaturated acylazoliums from 2-bromoenals underwent selective [3 + 3] annulation with one of the enantiomers of maleimide to furnish fused-dihydropyridinone (bearing axial/central chirality, up to 6:1 dr, >99:1 er) leaving the enantioenriched opposite enantiomer (up to >99:1 er). Studies on C–N bond rotation barrier and dependence on temperature are also provided.

The diverser eactivity of N-heterocyclic carbenes (NHCs) in organocatalysis is due to the possibility of different modeso fa ction. Although NHC-bounde nolates and dienolates are known, the related NHC-bound cross-conjugated aza-trienolates remain elusive. Herein,w ed emonstrate the NHC-catalyzed formal [6+ +2] annulation of nitrogen-containing heterocyclic aldehydes with a,a,a-trifluoroacetophenones leadingt ot he formation of versatile pyrrolooxazolones (29 examples). The catalytically generated cross-conjugated aza-trienolates (aza-fulvene type) underwent smooth [6+ +2] annulation with electrophilic ketones to afford the product in moderate to good yields under mild conditions. Preliminary DFT studies on the mechanism are also provided.Scheme1.Generation and reaction of various NHC-enolates.

Although the atroposelective synthesis of biaryls and related compounds bearing axially chiral C−C bonds is wellknown, the synthesis of axially chiral C−N bond-containing compounds is relatively less explored, and the construction of axially chiral N−N bonds has received only scant attention. Demonstrated herein is the N-heterocyclic carbene (NHC)-catalyzed selective amidation reaction, leading to the atroposelective synthesis of N−N axially chiral 3-amino quinazolinones. The NHC-catalyzed reaction of quinazolinones containing a free N−H moiety with α,β-unsaturated aldehydes under oxidative conditions furnished the atropisomeric quinazolinone derivatives under mild conditions and broad scope. Preliminary studies on experimental and density functional theory-based N−N rotational barrier determination are also presented.

Although the atroposelective synthesis of biaryls and related compounds bearing axially chiral C-C bonds are well-known, the synthesis of axially chiral C-N bond-containing compounds are relatively less explored, and the construction of axially chiral N-N bonds has received only scant attention. Demonstrated herein is the N-heterocyclic carbene (NHC)-catalyzed selective amidation reaction leading to the atroposelective synthesis of N-N axially chiral 3-amino quinazolinones. The NHC-catalyzed reaction of quinazolinones containing a free N-H moiety with -unsaturated aldehydes under oxidative conditions furnished the atropisomeric quinazolinone derivatives under mild conditions and broad scope. Preliminary studies on experimental and DFT-based N-N rotational barrier determination is also presented.