Asymmetric Organocatalysis in the Remote (3 + 2)-Cycloaddition to 4-(Alk-1-en-1-yl)-3-cyanocoumarins

The application of organocatalytic bifunctional activation in the remote (3 + 2)-cycloaddition between 4-(alk-1-en-1-yl)-3-cyanocoumarins and imines derived from salicylaldehyde is demonstrated. Products, bearing two biologically relevant units, have been obtained with good chemical and stereochemical efficiency. The stereochemical outcome of the process results from the application of a quinine-derived catalyst. Selected transformations of the cycloadducts leading to further chemical diversity have been demonstrated.

NHC-Activations on α-, β-, γ-, and Beyond

Over the recent decades, due to the special electronic characteristics and diverse reactivities, N-heterocyclic carbene (NHC) has received significant interest in organocatalyzed reactions. The formation of Breslow intermediates by NHC can convert into acyl anion equivalent, enolates, homoenolate, acyl azolium, and vinyl enolate etc., and the cycloaddition reactions of these species has attracted lots of attention. In this review, we focus on the summry of the development of NHC-activation of carbonyl carbon (or imine carbon) in situ, α-, β-, γ-, and beyond, and the cycloaddition reaction of these species.

Stereoselective N-Heterocyclic-Carbene-Catalyzed Formal [4 + 2] Cycloaddition: Access to Chiral Heterocyclic Cyclohexenones

The present study reports an asymmetric NHC-catalyzed formal [4 + 2] cycloaddition of heterocyclic alkenes containing a polarized double bond with an azolium-dienolate intermediate generated from α-bromo-α,β-unsaturated aldehydes without external oxidation of the Breslow intermediate. Heterocyclic cyclohexenones were produced in good isolated yields (typically about 90%) with good stereochemical outcomes (in most cases, dr > 20/1, and ee = 70-99%). The synthetic utility of the protocol was exemplified by the scope of heterocyclic alkenes.

Organocatalytic Asymmetric Approach to γ,δ-Functionalization of 3-Cyano-4-styrylcoumarins via Bifunctional Catalysis

A novel organocatalytic reaction cascade between 3-cyano-4-styrylcoumarins and 2-mercaptoacetophenones is described. It is based on stereocontrolled functionalization of cyanocoumarins proceeding in a sequence of thia-Michael/aldol/annulation reactions. This highly diastereo- and enantioselective reaction is realized by employing enantioselective bifunctional catalysis and exhibits a broad substrate scope and excellent functional group tolerance. The synthetic application involves the transformation of the imidoester group, thus opening access to biologically relevant coumarin and δ-lactone-fused products.

Recent development in asymmetric organocatalytic domino reactions involving 1,6-addition as a key step

This article highlights the significant development in stereoselective domino reactions involving 1,6-addition as a crucial step.

Asymmetric organocatalyzed synthesis of coumarin derivatives

Coumarin derivatives are essential scaffolds in medicinal and synthetic chemistry. Compounds of this class have shown important activities, such as anticancer and antiparasitic, besides the commercially available drugs. These properties led to the development of efficient and greener synthetic methods to achieve the 2H-chromen-2-one core. In this context, the advances in asymmetric organocatalyzed synthesis of coumarin derivatives are discussed in this review, according to the mode of activation of the catalyst.

Generation of azolium dienolates as versatile nucleophilic synthons via N-heterocyclic carbene catalysis

The recent advances in N-heterocyclic carbene (NHC)-catalyzed generation of azolium dienolates from different precursors and their synthetic applications for the construction of various valuable molecules are summarized comprehensively in this review.