@article { ISI:000368065300033, title = {Enantioselective synthesis of spirocyclohexadienones by NHC-catalyzed formal [3+3] annulation reaction of enals}, journal = {Angewandte Chemie-International Edition}, volume = {55}, number = {1}, year = {2016}, month = {JAN}, pages = {268-272}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {

The enantioselective synthesis of pyrazolone-fused spirocyclohexadienones was demonstrated by the reaction of alpha,beta-unsaturated aldehydes with alpha-arylidene pyrazolinones under oxidative N-heterocyclic carbene (NHC) catalysis. This atom-economic and formal [3+3] annulation reaction proceeds through a vinylogous Michael addition/spiroannulation/dehydrogenation cascade to afford spirocyclic compounds with an all-carbon quaternary stereocenter in moderate to good yields and excellent ee values. Key to the success of the reaction is the cooperative NHC-catalyzed generation of chiral alpha,beta-unsaturated acyl azoliums from enals, and base-mediated tandem generation of dienolate/enolate intermediates from pyrazolinones.

}, keywords = {annulation reactions, asymmetric catalysis, N-heterocyclic carbenes, organocatalysis, spiro compounds}, issn = {1433-7851}, doi = {10.1002/anie.201507802}, author = {Yetra, Santhivardhana Reddy and Mondal, Santigopal and Mukherjee, Subrata and Gonnade, Rajesh G. and Biju, Akkattu T.} } @article {45769, title = {N-Heterocyclic carbene-catalyzed aldol-lactonization of ketoacids via dynamic kinetic resolution}, journal = {ACS Catalysis}, volume = {7}, year = {2017}, month = {JUN}, pages = {3995-3999}, type = {Article}, abstract = {

N-Heteroryclic carbene (NHC)-catalyzed enantioselective aldol lactonization of acyclic ketoacids, proceeding via dynamic kinetic resolution, is presented. The carbene generated from the chiral anninoinclanol-derived triazolium salt in the presence of LiCl was the key for the success of this transformation. The reaction allowed the diastereoselective and enantioselective synthesis of cyclopentane-fused beta-lactones having three contiguous stereocenters. The reaction products are shown to undergo substrate-controlled beta-lactone opening in the presence of amines to afford succinimide derivatives with four contiguous stereocenters.

}, keywords = {aldol lactonization, beta-lactones, DKR strategies, ketoacids, N-heterocyclic carbenes, organocatalysis}, issn = {2155-5435}, doi = {10.1021/acscatal.7b00681}, author = {Mondal, Santigopal and Mukherjee, Subrata and Das, Tamal Kanti and Gonnade, Rajesh and Biju, Akkattu T.} } @article {47386, title = {NHC-catalyzed desymmetrization of N-aryl maleimides leading to the atroposelective synthesis of N-Aryl succinimides}, journal = {Angewandte Chemie-International Edition}, volume = {60}, year = {2021}, month = {MAY }, pages = {12264-12268}, type = {Article}, abstract = {

Although the construction of axially chiral C-C bonds leading to the atroposelective synthesis of biaryls and allied compounds are well-known, the related synthesis of compounds bearing axially chiral C-N bonds are relatively rare. Described herein is the N-heterocyclic carbene-catalyzed atroposelective synthesis of N-aryl succinimides having an axially chiral C-N bond via the desymmetrization of N-aryl maleimides. The NHC involved intermolecular Stetter-aldol cascade of dialdehydes with prochiral N-aryl maleimides followed by oxidation afforded N-aryl succinimides in good yields and ee values. Preliminary studies on rotation barrier for the C-N bond, the temperature dependence, and detailed DFT studies on mechanism are also provided.

}, keywords = {asymmetric catalysis, axial chirality, desymmetrization, N-heterocyclic carbenes, organocatalysis}, issn = {1433-7851}, doi = {10.1002/anie.202016938, Early Access Date = APR 2021}, author = {Barik, Soumen and Shee, Sayan and Das, Soumik and Gonnade, Rajesh G. and Jindal, Garima and Mukherjee, Subrata and Biju, Akkattu T.} }