@article {45481, title = {Enantioselective N-heterocyclic carbene-catalyzed cascade reaction for the synthesis of pyrroloquinolines via N-H functionalization of indoles}, journal = {Organic letters }, volume = {20}, year = {2018}, month = {NOV}, pages = {6998-7002}, type = {Article }, abstract = {Functionalization of the indole N-H bond for enantioselective synthesis of biologically important pyrroloquinoline derivatives has been reported under oxidative N-heterocyclic carbene catalysis conditions. The interception of catalytically generated chiral alpha,beta-unsaturated acylazoliums with the indole derivatives proceeds in an aza-Michael/Michael/lactonization sequence to deliver the pyrroloquinoline derivatives in good yields, diastereoselectivities, and enantioselectivities. The simultaneous enhancement of reactivity and selectivity observed in polar aprotic solvents is noteworthy.}, issn = {1523-7060}, doi = { 10.1021/acs.orglett.8b02820}, author = {Mukherjee, Subrata and Shee, Sayan and Poisson, Thomas and Besset, Tatiana and Biju, Akkattu T.} } @article {46782, title = {Enantioselective synthesis of tricyclic beta-lactones by NHC-catalyzed desymmetrization of cyclic 1,3-diketones}, journal = {Organic Letters}, volume = {22}, year = {2020}, month = {JUL}, pages = {5407-5411}, type = {Article}, abstract = {

The NHC-catalyzed desymmetrization of cyclic-1,3-diketones allowing the enantioselective construction of tricyclic beta-lactones with five contiguous stereocenters, including two quaternary stereocenters, has been developed. The mild and operationally simple addition of a-bromoenals to cyclopentane-1,3-diketone derivatives proceeds via the initial formation of chiral alpha,beta-unsaturated acylazolium intermediates and culminates in a cascade reaction, following the Michael-aldol-Iactonization pathway to deliver the beta-lactone derivatives in moderate to good yields and excellent selectivity.

}, issn = {1523-7060}, doi = {10.1021/acs.orglett.0c01756}, author = {Shee, Sayan and Mukherjee, Subrata and Gonnade, Rajesh G. and Biju, Akkattu T.} } @article {47626, title = {Enantioselective synthesis of 5,6-dihydroindolizines by N-heterocyclic carbene (NHC)-catalyzed core-structure-inspired strategy of azolium-enolate cascade}, journal = {Organic Letters}, volume = {23}, year = {2021}, month = {JUL }, pages = {5223-5228}, type = {Article}, abstract = {The core-structure motivated design has allowed the enantioselective synthesis of 5,6-dihydroindolizines via N-heterocyclic carbene (NHC) catalysis. The NHC-catalyzed reaction of alpha,beta-unsaturated aldehydes with the suitably substituted pyrrole derivatives proceed via the initial generation of alpha,beta-unsaturated acylazoliums from enals, and enolates from pyrroles and the reaction culminated in an efficient cascade process involving the Michael-aldol-lactonization-decarboxylation sequence to afford the products in reasonable yields and high selectivities. The method is further extended to the construction of spirocyclic 5,6-dihydroindolizines.}, issn = {1523-7060}, doi = {10.1021/acs.orglett.1c01761}, author = {Ghosh, Arghya and Shee, Sayan and Barik, Shilpa and Gonnade, Rajesh G. 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.} } @article {48040, title = {Dynamic kinetic resolution of gamma,gamma-disubstituted indole 2-carboxaldehydes via NHC-Lewis acid cooperative catalysis for the synthesis of tetracyclic epsilon-lactones}, volume = {13}, year = {2022}, month = {OCT}, pages = {11513-11518}, type = {Article}, abstract = {

The ubiquity of epsilon-lactones in various biologically active compounds inspired the development of efficient and enantioselective routes to these target compounds. Described herein is the enantioselective synthesis of indole-fused epsilon-lactones by the N-heterocyclic carbene (NHC)-Lewis acid cooperative catalyzed dynamic kinetic resolution (DKR) of in situ generated gamma,gamma-disubstituted indole 2-carboxaldehydes. The Bi(OTf)(3)-catalyzed Friedel-Crafts reaction of indole-2-carboxaldehyde with 2-hydroxy phenyl p-quinone methides generates gamma,gamma-disubstituted indole 2-carboxaldehydes, which in the presence of NHC and Bi(OTf)(3) afforded the desired tetracyclic epsilon-lactones in up to 93\% yield and \>99 : 1 er. Moreover, preliminary studies on the mechanism of this formal [4 + 3] annulation are also provided.

}, issn = {2041-6520}, doi = {10.1039/d2sc03745a}, author = {Balanna, Kuruva and Barik, Soumen and Shee, Sayan and Gonnade, Rajesh G. and Biju, Akkattu T.} } @article {48358, title = {Enantioselective synthesis of dihydrothiopyranones via NHC- catalyzed [3+3] annulation of 2-bromoenals with beta-oxodithioesters}, journal = {Organic Letters}, volume = {24}, year = {2022}, month = {DEC}, pages = {8848-8853}, type = {Article}, abstract = {

The N-heterocyclic carbene (NHC)-organocata-lyzed [3 + 3] annulation of 2-bromoenals with fi-oxodithioesters resulting in the enantioselective synthesis of dihydrothiopyranones is presented. The chiral a,fi-unsaturated acylazoliums generated from 2-bromoenals and carbenes underwent smooth interception with the sulfur nucleophiles to furnish the sulfur heterocycles in satisfactory yields/selectivity. The regioselective formation of dihydrothiopyranones over the competing dihydropyranones is noteworthy.

}, issn = {1523-7060}, doi = {10.1021/acs.orglett.2c03642}, author = {Barik, Shilpa and Shee, Sayan and Gonnade, Rajesh G. and Biju, Akkattu T.} } @article {48760, title = {NHC-catalyzed enantioselective synthesis of tetracyclic δ-lactones by (4+2) annulation of ortho-quinodimethanes with activated ketones}, journal = {Organic Letters}, volume = {25}, year = {2023}, month = {OCT }, pages = {7852-7857}, type = {Article}, abstract = {

The N-heterocyclic carbene (NHC)-catalyzed generation of ortho-quinodimethanes (o-QDMs) from 9H-fluorene-1-carbaldehydes followed by the interception with activated ketones resulting in the enantioselective synthesis of tetracyclic delta-lactones is presented. High diastereoselectivity of products, remote C-(sp(3))-H functionalization, broad substrate scope, and mild reaction conditions are the notable features of the present (4 + 2) annulation.

}, issn = {1523-7060}, doi = {10.1021/acs.orglett.3c03076}, author = {Sarkar, Deeptanu and Barik, Shilpa and Shee, Sayan and Gonnade, Rajesh G. and Biju, Akkattu T.} } @article {48752, title = {N-heterocyclic carbene-catalyzed atroposelective synthesis of N-N axially chiral 3-amino quinazolinones}, journal = {ACS Catalysis}, volume = {13}, year = {2023}, month = {JUN }, pages = {8752-8759}, type = {Article}, abstract = {

Although the atroposelective synthesisof biaryls and related compoundsbearing axially chiral C-C bonds is well-known, the synthesisof axially chiral C-N bond-containing compounds is relativelyless explored, and the construction of axially chiral N-N bondshas received only scant attention. Demonstrated herein is the N-heterocycliccarbene (NHC)-catalyzed selective amidation reaction, leading to theatroposelective synthesis of N-N axially chiral 3-amino quinazolinones.The NHC-catalyzed reaction of quinazolinones containing a free N-Hmoiety with \& alpha;,\& beta;-unsaturated aldehydes under oxidativeconditions furnished the atropisomeric quinazolinone derivatives undermild conditions and broad scope. Preliminary studies on experimentaland density functional theory-based N-N rotational barrierdetermination are also presented.

}, keywords = {amino quinazolinones, asymmetriccatalysis, axial chirality, N-heterocycliccarbenes, organocatalysis}, issn = {2155-5435}, doi = {10.1021/acscatal.3c01709}, author = {Balanna, Kuruva and Barik, Soumen and Barik, Shilpa and Shee, Sayan and Manoj, Niket and Gonnade, Rajesh G. and Biju, Akkattu T.} }