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Tricyclic benzopyrans are medicinally important biologically active compounds. Synthesis of a series of tricyclic benzopyrans derivatives via N-Heterocyclic carbene (NHC) catalyzed annulation of enals to α-methylidenetetralones/chromanones is described. This reaction afforded the benzopyrans in high yield with aromatic as well as aliphatic enals.

A nucleophilic heterocyclic carbene-mediated intramolecular homoenolate reaction strategy for the efficient synthesis of cyclopentene-fused macrocycles is reported.

An unexpected transformation of 1,6-diarylhexa-1,5-diene-3,4-diones (cinnamils) to 2,3,8-triaryl vinyl fulvenes via N-Heterocyclic Carbene (NHC) catalysis is reported. Mechanistic as well as synthetic novelty is the hallmark of this reaction.

Nucleophilic heterocyclic carbene (NHC)-catalyzed ­annulation strategy has been utilized for the efficient synthesis of styrenyl-substituted cyclopentenes from 2,4-dienones.

The facile synthesis of 1,3,4-trisubstituted cyclopentenes via homoenolate annulation of enals with heterocycle substituted chalcones is described.

A stereoselective Michael addition of homoenolate, generated from enals by nucleophilic heterocyclic carbene (NHC) catalysis, to beta-nitrostyrenes is reported for the first time. The products of this reaction obtained in good yields are of potential value in the synthesis of a variety of acyclic and heterocyclic compounds.

Tricyclic benzopyrans are medicinally important biologically active compounds. Synthesis of a series of tricyclic benzopyrans derivatives via N-Heterocyclic carbene (NHC) catalyzed annulation of enals to α-methylidenetetralones/chromanones is described. This reaction afforded the benzopyrans in high yield with aromatic as well as aliphatic enals.

Aryl, hetaryl, alkyl and alkenyl enals are reacting with 2-aroylidene substituted alkylbenzofuran-3-ones providing the corresponding products as single diastereomers.

A nucleophilic heterocyclic carbene-mediated intramolecular homoenolate reaction strategy for the efficient synthesis of cyclopentene-fused macrocycles is reported.

Homoenolate annulation of vinyl ketones led to the synthesis of dihydropyranones in contrast to cyclopentenes obtained by the homoenolate annulation of chalcones, another class of α,β-unsaturated ketones.

A nucleophilic heterocyclic carbene mediated homoenolate annulation of enals to aurone analogs leading to the efficient synthesis of cyclopentene-fused spirobenzofuran-3-ones is reported.

Under optimized conditions the uncommon cascade reaction gives vinyl fulvenes and ortho-terphenyl derivatives as by-products.

A facile NHC-mediated reaction of aromatic aldehydes with carbon dioxide leading to carboxylic acids is described. The present protocol is mechanistically important, and it can serve as a tool for the sequestration of carbon dioxide.

Transient zwitterion generated from allenoate and isoquinoline was successfully intercepted with cyanoacrylates and arylidenemalononitriles to devise a novel multicomponent reaction under mild conditions.

A simple NHC-catalyst promotes the reaction of enals with dienones to give unexpected cyclopentene derivatives (III).

Comparable yields of (II) are obtained regardless whether the E/Z-mixtures of the substrates are used or pure isomers.

A nucleophilic heterocyclic carbene mediated intramolecular homoenolate reaction strategy for the efficient synthesis of 4-alkyl substituted coumarins is described.

Transient zwitterions generated from dimethyl allenedicarboxylate and isoquinoline were successfully intercepted with 2-oxo-1H-indol-3-ylidenes to result in a facile multicomponent reaction under mild conditions.

The facile synthesis of 1,3,4-trisubstituted cyclopentenes via homoenolate annulation of enals with heterocycle substituted chalcones is described.

The homoenolate annulation to vinyl ketones gives dihydropyranone derivatives in contrast to cyclopentenes resulting from homoenolate reaction of chalcones.

Homoenolate is a reactive intermediate that possesses an anionic or nucleophilic carbon β to a carbonyl group or its synthetic equivalent. The recent discovery that homoenolates can be generated from α,β-unsaturated aldehydesviaN-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.

An unexpected transformation of 2H-chromene-3-carboxaldehydes to coumarin derivatives, mediated by NHC, is reported.

Homoenolate is a reactive intermediate that possesses an anionic or nucleophilic carbon β to a carbonyl group or its synthetic equivalent. The recent discovery that homoenolates can be generated from α,β-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.

An unexpected transformation of 2H-chromene-3-carboxaldehydes to coumarin derivatives, mediated by NHC, is reported.

The reaction affords the corresponding carboxylic acids instead of the expected glyoxylic acids (III) (mechanism).

The presented quinone—nitrone reactions are considered as a special case among quinone-1,3-dipole cycloaddition reactions.

Homoenolate generated from α,β-unsaturated aldehydes by NHC catalysis underwent facile addition to conjugated sulfonimines, generated in situ, and subsequent methanolysis to afford protected GABA derivatives stereoselectively and in high yields, thus constituting a novel pseudo four component reaction.

A stereoselective Michael addition of homoenolate, generated from enals by nucleophilic heterocyclic carbene (NHC) catalysis, to β-nitrostyrenes is reported for the first time. The products of this reaction obtained in good yields are of potential value in the synthesis of a variety of acyclic and heterocyclic compounds.

The presented quinone—nitrone reactions are considered as a special case among quinone-1,3-dipole cycloaddition reactions.

Transient zwitterion generated from allenoate and isoquinoline was successfully intercepted with cyanoacrylates and arylidenemalononitriles to devise a novel multicomponent reaction under mild conditions.

Homoenolate generated from alpha,beta-unsaturated aldehydes by NHC catalysis underwent facile addition to conjugated sulfonimines, generated in situ, and subsequent methanolysis to afford protected GABA derivatives stereoselectively and in high yields, thus constituting a novel pseudo four component reaction.

Transient zwitterions generated from dimethyl allenedicarboxylate and isoquinoline were successfully intercepted with 2-oxo-1H-indol-3-ylidenes to result in a facile multicomponent reaction under mild conditions.