00911nas a2200181 4500008004100000245011800041210006900159260000800228300001400236490000700250520024600257100001600503700002200519700002200541700001700563700002200580856012700602 2006 eng d00aEngaging zwitterions in carbon-carbon and carbon-nitrogen bond- forming reactions: a promising synthetic strategy0 aEngaging zwitterions in carboncarbon and carbonnitrogen bond for cJUN a520–5300 v393 a

An Account of carbon−carbon and carbon−nitrogen bond-forming reactions mediated by zwitterions generated by the addition of organic nucleophiles to activated unsaturated systems highlighting their synthetic potential is presented.

1 aNair, Vijay1 aMenon, Rajeev, S.1 aSreekanth, A., R.1 aAbhilash, N.1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/engaging-zwitterions-carbon-carbon-and-carbon-nitrogen-bond-forming-reactions-promising01044nas a2200169 4500008004100000245009100041210006900132260000800201300001400209520034500223653009800568100001600666700002900682700002200711700002400733856011700757 2007 eng d00aEfficient higher-order cycloaddition reactions of 8,8-dicyanoheptafulvenes with dienes0 aEfficient higherorder cycloaddition reactions of 88dicyanoheptaf cJUN a1833-18363 a

The cycloaddition reactions of 8,8-dicyanoheptafulvene with electron-rich dienes afforded the higher order cycloaddition products in excellent yields. With cyclic dienes as well as dimeth­oxybutadiene the [8+2] adducts were obtained exclusively. With methyl- and dimethylbutadienes the [6+4] adducts were the only products isolated.

10acycloadditions - bicyclic compounds - polycycles - di­cyanoheptafulvene - tetrahydroazulenes1 aNair, Vijay1 aAbhilash, Gopalakrishnan1 aBiju, Akkattu, T.1 aEringathodi, Suresh uhttps://library.ncl.res.in/content/efficient-higher-order-cycloaddition-reactions-88-dicyanoheptafulvenes-dienes01045nas a2200169 4500008004100000022001400041245013200055210006900187260007100256300001400327490000700341520033200348100002200680700002200702700001900724856013200743 2011 eng d a1523-706000aEfficient synthesis of benzofuranones: N-heterocyclic carbene (NHC)/base-catalyzed hydroacylation-stetter-rearrangement cascade0 aEfficient synthesis of benzofuranones Nheterocyclic carbene NHCb a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcOCT a5624-56270 v133 a

A N-heterocyclic carbene/base-catalyzed cascade reaction leading to the formation of functionalized benzofuranones is reported. The reaction proceeds via an intramolecular hydroacylation of unactivated alkynes followed by an intermolecular Stetter reaction and a base-catalyzed chromanone to benzofuranone rearrangement.

1 aPadmanaban, Mohan1 aBiju, Akkattu, T.1 aGlorius, Frank uhttps://library.ncl.res.in/content/efficient-synthesis-benzofuranones-n-heterocyclic-carbene-nhcbase-catalyzed-hydroacylation-001874nas a2200217 4500008004100000022001400041245011200055210006900167260011000236300001400346490000700360520102000367100001601387700002201403700002201425700001701447700002201464700001401486700002501500856013101525 2011 eng d a0306-001200aEmploying homoenolates generated by NHC catalysis in carbon-carbon bond-forming reactions: state of the art0 aEmploying homoenolates generated by NHC catalysis in carboncarbo aTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLANDbROYAL SOC CHEMISTRYcJUL a5336-53460 v403 a

Homoenolate is a reactive intermediate that possesses an anionic or nucleophilic carbon beta to a carbonyl group or its synthetic equivalent. The recent discovery that homoenolates can be generated from alpha,beta-unsaturated aldehydes via N-Heterocyclic Carbene (NHC) catalysis has led to the development of a number of new reactions. A majority of such reactions include the use of carbon-based electrophiles, such as aldehydes, imines, enones, dienones etc. resulting in the formation of a variety of annulated as well as acyclic products. The easy availability of chiral NHCs has allowed the development of very efficient enantioselective variants of these reactions also. The tolerance showed by NHCs towards magnesium and titanium based Lewis acids has been exploited in the invention of cooperative catalytic processes. This tutorial review focuses on these and other types of homoenolate reactions reported recently, and in the process, updates the previous account published in 2008 in this journal.

1 aNair, Vijay1 aMenon, Rajeev, S.1 aBiju, Akkattu, T.1 aSinu, C., R.1 aPaul, Rony, Rajan1 aJose, Anu1 aSreekumar, Vellalath uhttps://library.ncl.res.in/content/employing-homoenolates-generated-nhc-catalysis-carbon-carbon-bond-forming-reactions-state-001351nas a2200157 4500008004100000245008900041210006900130260000800199300001600207490000700223520079000230100002201020700001701042700001901059856011501078 2011 eng d00aExtending nhc-catalysis: reaction of aldehydes with unconventional reaction partners0 aExtending nhccatalysis reaction of aldehydes with unconventional cJUL a1182–11950 v443 a

Transition metal catalysis is a powerful means of effecting organic reactions, but it has some inherent drawbacks, such as the cost of the catalyst and the toxicity of the metals. Organocatalysis represents an attractive alternative and, in some cases, offers transformations unparalleled in metal catalysis. Unique transformations are a particular hallmark of N-heterocyclic carbene (NHC) organocatalysis, a versatile method for which a number of modes of action are known. The NHC-catalyzed umpolung (that is, the inversion of polarity) of electrophilic aldehydes, through formation of the nucleophilic Breslow intermediate, is probably the most important mode of action. In this Account, we discuss the reaction of Breslow intermediates with unconventional reaction partners.

1 aBiju, Akkattu, T.1 aKuhl, Nadine1 aGlorius, Frank uhttps://library.ncl.res.in/content/extending-nhc-catalysis-reaction-aldehydes-unconventional-reaction-partners01086nas a2200157 4500008004100000245010500041210006900146260000800215300001600223490000700239520048000246100002300726700002900749700002200778856012800800 2012 eng d00aEfficient diels-alder reaction of 1,2-benzoquinones with arynes and its utility in one-pot reactions0 aEfficient dielsalder reaction of 12benzoquinones with arynes and cDEC a6238–62410 v143 a

A new protocol for the efficient Diels–Alder reaction of 1,2-benzoquinones with arynes is reported. The aryne generated by the fluoride-induced 1,2-elimination of 2-(trimethylsilyl)aryl triflates undergoes a facile Diels–Alder reaction with 1,2-benzoquinones, affording the dioxobenzobicyclooctadienes in moderate to excellent yields. In addition, this methodology has been applied to the one-pot synthesis of benzoquinoxalinobarrelene and naphthalene derivatives.

1 aKaicharla, Trinadh1 aBhojgude, Sachin, Suresh1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/efficient-diels-alder-reaction-12-benzoquinones-arynes-and-its-utility-one-pot-reactions01049nas a2200169 4500008004100000245009600041210006900137260000800206300001600214490000700230520041600237100001700653700003300670700002900703700002200732856012500754 2012 eng d00aEfficient synthesis of gamma-keto sulfones by NHC-catalyzed intermolecular stetter reaction0 aEfficient synthesis of gammaketo sulfones by NHCcatalyzed interm cMAY a2830–28330 v143 a

The N-heterocyclic carbene-catalyzed intermolecular Stetter reaction of aldehydes with α,β-unsaturated sulfones allows the atom-economic and selective formation of γ-keto sulfones in good yields. Key to the success of this unique transition-metal-free carbon–carbon bond-forming reaction is the right choice of the NHC precursor and base. The reaction tolerates a broad range of different aldehydes.

1 aBhunia, Anup1 aYetra, Santhivardhana, Reddy1 aBhojgude, Sachin, Suresh1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/efficient-synthesis-gamma-keto-sulfones-nhc-catalyzed-intermolecular-stetter-reaction01102nas a2200169 4500008004100000022001400041245008800055210006900143260007100212300001400283490000700297520043500304100002900739700002300768700002200791856011900813 2013 eng d a1523-706000aEmploying arynes in transition-metal-free monoarylation of aromatic tertiary amines0 aEmploying arynes in transitionmetalfree monoarylation of aromati a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcNOV a5452-54550 v153 a

The highly monoselective N-arylation of aromatic tertiary amines using a transition-metal-free approach using arynes has been developed. The reaction afforded functionalized diaryl amines in moderate to excellent yield. High levels of functional group compatibility especially with halogen containing substrates, dyes and donor-acceptor systems, and high yields of products are the notable features of the present reaction.

1 aBhojgude, Sachin, Suresh1 aKaicharla, Trinadh1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/employing-arynes-transition-metal-free-monoarylation-aromatic-tertiary-amines-001266nas a2200181 4500008004100000022001400041245007800055210006900133260011000202300001400312490000700326520054800333100002300881700003300904700001400937700002200951856011100973 2013 eng d a1463-926200aEngaging isatins in solvent-free, sterically congested passerini reaction0 aEngaging isatins in solventfree sterically congested passerini r aTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLANDbROYAL SOC CHEMISTRYcAPR a1608-16140 v153 a

A facile, atom-economic and environmentally-benign protocol for the synthesis of biologically important oxindole derivatives in high yields has been demonstrated by employing isatins as carbonyl compound surrogates in a Passerini reaction carried out under solvent-free conditions. Moreover, electron-deficient phenols can also be used as the acid component in this reaction. In addition, the synthetic utility of the present methodology was examined by the one-pot synthesis of oxindoles with a free -OH group at the benzylic position.

1 aKaicharla, Trinadh1 aYetra, Santhivardhana, Reddy1 aRoy, Tony1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/engaging-isatins-solvent-free-sterically-congested-passerini-reaction-001159nas a2200181 4500008004100000022001400041245010600055210006900161260007100230300001200301490000700313520043900320100002900759700001700788700002400805700002200829856012600851 2014 eng d a1523-706000aEfficient synthesis of 9-aryldihydrophenanthrenes by a cascade reaction involving arynes and styrenes0 aEfficient synthesis of 9aryldihydrophenanthrenes by a cascade re a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcFEB a676-6790 v163 a

A mild, general, and transition-metal-free protocol for the synthesis of 9,10-dihydrophenanthrenes is reported. The aryne generated by the fluoride-induced,1,2-elimination of 2-(trimethylsilyl)aryl triflates undergoes an efficient cascade reaction initiated by the Diels-Alder reaction with the differently substituted styrenes leading to the formation of 9-aryl-9,10-dihydrophenanthrene derivatives in moderate to good yields.

1 aBhojgude, Sachin, Suresh1 aBhunia, Anup1 aGonnade, Rajesh, G.1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/efficient-synthesis-9-aryldihydrophenanthrenes-cascade-reaction-involving-arynes-and-001218nas a2200157 4500008004100000245009700041210006900138260000800207300001200215490000700227520058500234653007400819100001700893700002200910856012800932 2014 eng d00aEmploying arynes in transition-metal-free, N-heterocycles initiated multicomponent reactions0 aEmploying arynes in transitionmetalfree Nheterocycles initiated  cJAN a608-6140 v253 a

Transition-metal-free multicomponent reactions involving arynes, N-heterocycles, and various carbonyl compounds have been reported. With (iso)quinoline as the nucleophile and carbonyl compounds, such as aldehydes, ketones, and N-substituted isatins as electrophiles, the reaction afforded oxazino (iso)quinoline derivatives and the reaction proceeded via 1,4-dipolar intermediates. Interestingly, when the nucleophilic trigger used is pyridine, the reaction furnished indolin-2-one derivatives, and it is probable that the reaction proceeds via a pyridylidene intermediate.

10aarynes - multicomponent reaction - oxindoles - pyridines - quinolines1 aBhunia, Anup1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/employing-arynes-transition-metal-free-n-heterocycles-initiated-multicomponent-reactions01121nas a2200181 4500008004100000022001400041245013800055210006900193260000800262300001400270490000700284520042000291100003300711700002300744700002400767700002200791856012600813 2015 eng d a1523-706000aEnantioselective synthesis of functionalized pyrazoles by NHC-catalyzed reaction of pyrazolones with alpha,beta-unsaturated aldehydes0 aEnantioselective synthesis of functionalized pyrazoles by NHCcat cMAR a1417-14200 v173 a

The N-heterocyclic carbene (NHC)-organocatalyzed enantioselective annulation reaction of pyrazolones with alpha,beta-unsaturated aldehydes proceeding via the chiral alpha,beta-unsaturated acyl azolium intermediates under oxidative conditions is presented. The reaction afforded dihydropyranone-fused pyrazoles in moderate to good yields and good er values under operationally simple and base-free conditions.

1 aYetra, Santhivardhana, Reddy1 aMondal, Santigopal1 aSuresh, Eringathodi1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/enantioselective-synthesis-functionalized-pyrazoles-nhc-catalyzed-reaction-pyrazolones05205nas a2200181 4500008004100000245012200041210007100163260000800234300001400242490000700256520442000263653003504683653009704718100002904815700001704844700002204861856014004883 2016 eng d00aEmploying arynes in diels–alder reactions and transition-metal-free multicomponent coupling and arylation reactions0 aEmploying arynes in diels–alder reactions and transitionmetalfre cSEP a1658-16700 v493 a

Conspectus

Arynes are highly reactive intermediates having several applications in organic synthesis for the construction of various ortho-disubstituted arenes. Traditionally, arynes are generated in solution from haloarenes under strongly basic conditions. However, the scopes of many of the aryne reactions are limited because of the harsh conditions used for their generation. The renaissance of interest in aryne chemistry is mainly due to the mild conditions for their generation by the fluoride-induced 1,2-elimination of 2-(trimethylsilyl)aryl triflates. This Account is focused on the Diels–Alder reaction of arynes and their transition-metal-free application in multicomponent couplings as well as arylation reactions.

The Diels–Alder reaction of arynes is a powerful tool for constructing benzo-fused carbocycles and heterocycles. In 2012, we developed an efficient, broad-scope, and scalable Diels–Alder reaction of pentafulvenes with arynes affording benzonorbornadiene derivatives. Subsequently, we accomplished the Diels–Alder reaction of arynes with dienes such as 1,2-benzoquinones and tropones. Moreover, we uncovered a transition-metal-free protocol for the synthesis of 9,10-dihydrophenanthrenes by the reaction of arynes with styrenes that proceeds via a Diels–Alder/ene-reaction cascade. In addition, we demonstrated the reaction of arynes with indene/benzofurans, which proceeds via a tandem [4 + 2]/[2 + 2] sequence.

Multicomponent coupling (MCC) involving arynes mainly comprises the initial addition of a nucleophile to the aryne followed by interception of the aryl anion intermediate with an electrophile (provided the nucleophilic and electrophilic moieties do not belong to the same molecule). We have disclosed aryne MCCs initiated by N-heterocycles such as (iso)quinoline, pyridine, and aziridines. When (iso)quinoline is used as the nucleophilic trigger and N-substituted isatin as the third component, the reaction affords spirooxazino(iso)quinolines via 1,4-dipolar intermediates. Unexpectedly, using pyridine affords indolin-2-ones, where the reaction proceeds via the pyridylidene intermediate. Additionally, we developed the phosphine-triggered aryne MCCs for the synthesis of functionalized benzooxaphospholes. In another phase of our work, we studied the synthetic utility of CO2 as a one-carbon synthon in aryne MCCs for the synthesis of phthalimides.

Engaging arynes as an aryl source is one of the transition-metal-free methods for arylation reactions. We have demonstrated the N-arylation of aromatic tertiary amines and O-arylation of aliphatic alcohols using arynes.

It is anticipated that the chemistry of arynes will continue to prosper and will lead to surprising developments for the synthesis of various 1,2-disubstituted arenes of molecular complexity and structural diversity. Future challenges in this area include the utility of arynes in enantioselective transformations and the synthesis and reactions of exotic heterocyclic arynes.

10a2-Benzoquinones; Cycloaddition10aFacile N-arylation; O-arylation; One-Pot; Aldehydes; Benzyne; Amines; Heterocycles; Acids; 11 aBhojgude, Sachin, Suresh1 aBhunia, Anup1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/employing-arynes-diels%E2%80%93alder-reactions-and-transition-metal-free-multicomponent-coupling-and01459nas a2200205 4500008004100000022001400041245009900055210006900154260007200223300001000295490000600305520068100311100001400992700002901006700002301035700002601058700001801084700002201102856012901124 2016 eng d a2052-412900aEmploying carboxylic acids in aryne multicomponent coupling triggered by aziridines/azetidines0 aEmploying carboxylic acids in aryne multicomponent coupling trig aPO BOX 1-18, NANKANG, TAIPEI 115, TAIWANbCHINESE CHEMICAL SOCcNOV a71-760 v33 a

The transition-metal-free aryne multicomponent coupling (MCC) involving carboxylic acids initiated by aziridines/azetidines has been reported. The use of aziridines as nucleophiles afforded N-aryl beta-amino alcohol derivatives and the application of azetidines as nucleophilic triggers furnished N-aryl gamma-amino alcohol derivatives in moderate to good yields. These reactions proceed under mild conditions and result in the formation of a new carbon-nitrogen bond and a new carbon-oxygen bond. The utility of carboxylic acids in aryne MCCs has been demonstrated, and the synthetic potential of phenols as acid surrogates in the present aryne MCCs has been realized.

1 aRoy, Tony1 aBhojgude, Sachin, Suresh1 aKaicharla, Trinadh1 aThangaraj, Manikandan1 aGarai, Bikash1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/employing-carboxylic-acids-aryne-multicomponent-coupling-triggered-aziridinesazetidines-001701nas a2200253 4500008004100000022001400041245011600055210006900171260007500240300001200315490000700327520074400334653002501078653002501103653002801128653002001156653002001176100003301196700002301229700002301252700002401275700002201299856012601321 2016 eng d a1433-785100aEnantioselective synthesis of spirocyclohexadienones by NHC-catalyzed formal [3+3] annulation reaction of enals0 aEnantioselective synthesis of spirocyclohexadienones by NHCcatal aPOSTFACH 101161, 69451 WEINHEIM, GERMANYbWILEY-V C H VERLAG GMBHcJAN a268-2720 v553 a

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.

10aannulation reactions10aasymmetric catalysis10aN-heterocyclic carbenes10aorganocatalysis10aspiro compounds1 aYetra, Santhivardhana, Reddy1 aMondal, Santigopal1 aMukherjee, Subrata1 aGonnade, Rajesh, G.1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/enantioselective-synthesis-spirocyclohexadienones-nhc-catalyzed-formal-33-annulation-101162nas a2200169 4500008004100000245011100041210007000152260000800222490000700230520051000237100002300747700002300770700002200793700002400815700002200839856013100861 2017 eng d00aEnantioselective synthesis of functionalized β-lactones by NHC-catalyzed aldol lactonization of ketoacids0 aEnantioselective synthesis of functionalized βlactones by NHCcat cAUG0 v823 aN-Heterocyclic carbene (NHC)-catalyzed intramolecular aldol lactonization of readily available ketoacids leading to the enantioselective synthesis of cyclopentane-fused β-lactones is presented. The reaction proceeds via the generation of NHC-bound enolate intermediates formed from the ketoacids in the presence of the peptide coupling reagent HATU and NHC generated from the chiral triazolium salt. The functionalized β-lactones are formed under mild conditions in high yields and enantioselectivities.1 aMondal, Santigopal1 aMukherjee, Subrata1 aDas, Tamal, Kanti1 aGonnade, Rajesh, G.1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/enantioselective-synthesis-functionalized-%CE%B2-lactones-nhc-catalyzed-aldol-lactonization01711nas a2200193 4500008004100000245015800041210007000199260000800269300001600277490000700293520094900300100002301249700001701272700001701289700003101306700002701337700002201364856013101386 2017 eng d00aEnantioselective synthesis of spiro γ-butyrolactones by N-heterocyclic carbene (NHC)-catalyzed formal [3+2] annulation of enals with 3-hydroxy oxindoles0 aEnantioselective synthesis of spiro γbutyrolactones by Nheterocy cFEB a2013 - 20190 v163 aThe N-heterocyclic carbene (NHC)-catalyzed enantioselective formal [3 + 2] annulation of α,β-unsaturated aldehydes with 3-hydroxy oxindoles is presented. Under oxidative conditions using the bisquinone oxidant, the reaction resulted in the synthesis of spiro γ-butyrolactones in moderate to good yields, enantioselectivity and diastereoselectivity. The reaction likely proceeds via the generation of the NHC-bound α,β-unsaturated acylazolium intermediate from enals, which was intercepted by the dioxindoles in a formal [3 + 2] pathway to form the spirocyclic compounds. However, a deeper mechanistic investigation revealed that the reaction can also proceed via the homoenolate intermediate. In this case, the dioxindole was oxidized to the corresponding isatin derivative using traces of air under basic conditions, and was intercepted with the NHC-bound homoenolate intermediate in a formal [3 + 2] pathway to afford the spiro compound.1 aMukherjee, Subrata1 aJoseph, Sumi1 aBhunia, Anup1 aGonnade, Rajesh, Ghanshyam1 aReddy, Santhi, Vardhan1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/enantioselective-synthesis-spiro-%CE%B3-butyrolactones-n-heterocyclic-carbene-nhc-catalyzed01111nas a2200157 4500008004100000245010500041210006900146260000800215300001600223490000700239520052200246100002200768700001700790700002200807856012400829 2018 eng d00aEmploying arynes for the generation of aryl anion equivalents and subsequent reaction with aldehydes0 aEmploying arynes for the generation of aryl anion equivalents an cSEP a11333-113400 v833 a

Arynes are highly reactive intermediates, which are utilized for the electrophilic arylation of various X-H bonds (X = O, N, S etc.). Herein, a new synthetic strategy is demonstrated, where arynes are converted into aryl anion equivalents by treatment with phosphines and a base. The addition of phosphines to arynes form the phosphonium salts, which in the presence of a carbonate base generates the aryl anion equivalent. Subsequent addition of the aryl anions with aldehydes afforded the secondary alcohols.

1 aGaykar, Rahul, N.1 aBhunia, Anup1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/employing-arynes-generation-aryl-anion-equivalents-and-subsequent-reaction-aldehydes01313nas a2200193 4500008004100000022001400041245014700055210006900202260000800271300001400279490000700293520060200300100002300902700001600925700002000941700002000961700002200981856011601003 2018 eng d a1523-706000aEnantioselective N-heterocyclic carbene-catalyzed cascade reaction for the synthesis of pyrroloquinolines via N-H functionalization of indoles0 aEnantioselective Nheterocyclic carbenecatalyzed cascade reaction cNOV a6998-70020 v203 aFunctionalization 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.1 aMukherjee, Subrata1 aShee, Sayan1 aPoisson, Thomas1 aBesset, Tatiana1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/enantioselective-n-heterocyclic-carbene-catalyzed-cascade-reaction-synthesis01281nas a2200181 4500008004100000022001400041245011600055210006900171260000800240300001400248490000700262520061400269100001600883700002300899700002400922700002200946856013100968 2020 eng d a1523-706000aEnantioselective synthesis of tricyclic beta-lactones by NHC-catalyzed desymmetrization of cyclic 1,3-diketones0 aEnantioselective synthesis of tricyclic betalactones by NHCcatal cJUL a5407-54110 v223 a

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.

1 aShee, Sayan1 aMukherjee, Subrata1 aGonnade, Rajesh, G.1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/enantioselective-synthesis-tricyclic-beta-lactones-nhc-catalyzed-desymmetrization-cyclic-1301399nas a2200193 4500008004100000022001400041245015900055210006900214260000900283300001400292490000700306520066400313100001800977700001600995700001801011700002401029700002201053856013001075 2021 eng d a1523-706000aEnantioselective synthesis of 5,6-dihydroindolizines by N-heterocyclic carbene (NHC)-catalyzed core-structure-inspired strategy of azolium-enolate cascade0 aEnantioselective synthesis of 56dihydroindolizines by Nheterocyc cJUL  a5223-52280 v233 aThe 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.1 aGhosh, Arghya1 aShee, Sayan1 aBarik, Shilpa1 aGonnade, Rajesh, G.1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/enantioselective-synthesis-56-dihydroindolizines-n-heterocyclic-carbene-nhc-catalyzed-core01199nas a2200181 4500008004100000022001400041245013300055210006900188260000800257300001400265490000700279520052300286100001800809700001600827700002400843700002200867856012800889 2022 eng d a1523-706000aEnantioselective synthesis of dihydrothiopyranones via NHC- catalyzed [3+3] annulation of 2-bromoenals with beta-oxodithioesters0 aEnantioselective synthesis of dihydrothiopyranones via NHC catal cDEC a8848-88530 v243 a

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.

1 aBarik, Shilpa1 aShee, Sayan1 aGonnade, Rajesh, G.1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/enantioselective-synthesis-dihydrothiopyranones-nhc-catalyzed-33-annulation-2-bromoenals