N-Heterocyclic Carbene-Catalyzed Homoenolate Additions with N-Aryl Ketimines as Electrophiles: Efficient Synthesis of Spirocyclic γ-Lactam Oxindoles

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.

Reductive Alkenylation of Ketimines via Hydride Transfer from Aldehydes

The first direct N-heterocyclic carbene (NHC)-catalyzed preparation of allylic amines bearing a quaternary center (α-tertiary amine) from isatin-derived ketimines in the presence of vinyl selenones and aldehydes is reported. This multicomponent reaction is expected to proceed via unprecedented in situ reduction of imines through a hydride transfer from the aldehydes.

An N-heterocyclic carbene-catalyzed enantioselective [3 + 2] annulation of enals with propargylic imines: access to γ,γ-disubstituted pyrrolidin-2-ones bearing quaternary stereogenic centers

An N-heterocyclic carbene-catalyzed enantioselective [3 + 2] annulation of enals with propargylic imines for the construction of γ,γ-disubstituted pyrrolidin-2-ones was developed.

Synthesis of functionalized 3,2′-pyrrolidinyl spirooxindoles via domino 1,6-addition/annulation reactions of para-quinone methides and 3-chlorooxindoles

A highly efficient diastereoselective [4 + 1] cycloaddition of ortho-tosylaminophenyl-substituted p-QMs with 3-chlorooxindoles has been developed to afford 3,2′-pyrrolidinyl spirooxindoles.

Mannich-type allylic C–H functionalization of enol silyl ethers under photoredox–thiol hybrid catalysis

The synergy of an Ir-based photosensitizer with mild oxidizing ability and a thiol catalyst enables efficient allylic C–H functionalization of enol silyl ethers with imines under visible light irradiation.

New Developments of the Principle of Vinylogy as Applied to π-Extended Enolate-Type Donor Systems

The principle of vinylogy states that the electronic effects of a functional group in a molecule are possibly transmitted to a distal position through interposed conjugated multiple bonds. As an emblematic case, the nucleophilic character of a π-extended enolate-type chain system may be relayed from the legitimate α-site to the vinylogous γ, ε, ..., ω remote carbon sites along the chain, provided that suitable HOMO-raising strategies are adopted to transform the unsaturated pronucleophilic precursors into the reactive polyenolate species. On the other hand, when "unnatural" carbonyl ipso-sites are activated as nucleophiles (umpolung), vinylogation extends the nucleophilic character to "unnatural" β, δ, ... remote sites. Merging the principle of vinylogy with activation modalities and concepts such as iminium ion/enamine organocatalysis, NHC-organocatalysis, cooperative organo/metal catalysis, bifunctional organocatalysis, dicyanoalkylidene activation, and organocascade reactions represents an impressive step forward for all vinylogous transformations. This review article celebrates this evolutionary progress, by collecting, comparing, and critically describing the achievements made over the nine year period 2010-2018, in the generation of vinylogous enolate-type donor substrates and their use in chemical synthesis.

Enantioselective (3+2) cycloaddition via N-heterocyclic carbene-catalyzed addition of homoenolates to cyclic N-sulfonyl trifluoromethylated ketimines: synthesis of fused N-heterocycle γ-lactams

An enantioselective (3+2) cycloaddition of enals and cyclic N-sulfonyl trifluoromethyl ketimines via N-heterocyclic carbene-catalyzed homoenolate addition is described. This reaction can efficiently construct fused N-heterocycle γ-lactams bearing two adjacent chiral centers with >20 : 1 dr and 94-99% ee, with one chiral center as a trifluoromethylated α-tetrasubstituted carbon stereocenter.

Catalytic Asymmetric γ-Lactam Synthesis from Enolisable Anhydrides and Imines

An anion-binding approach to the problem of preparing enantioenriched γ-lactams from enolisable anhydrides and imines is reported. A simple bisurea catalyst promotes the cycloaddition between α-aryl succinic anhydrides and either PMP- or benzhydryl-protected aldimines to provide γ-lactams with two contiguous stereocentres (one quaternary) with complete diastereocontrol and high to excellent enantioselectivity for the first time. A DFT study has provided insight into the catalyst mode of action and the origins of the observed stereocontrol.

Methyl isocyanide as a convertible functional group for the synthesis of spirocyclic oxindole γ-lactams via post-Ugi-4CR/transamidation/cyclization in a one-pot, three-step sequence

The synthesis of spiro[indoline-3,2'-pyrrole]-2,5'(1'H)-diones and spiro[indoline-3,2'-pyrrolidine]-2,5'-diones, via a post-Ugi-domino transamidation/cyclization sequential process, has been achieved in three sequential steps utilizing a one-pot reaction protocol. The variation in carboxylic acid substrates allows for the generation of new chiral racemic quaternary carbon centers under basic conditions providing molecular diversity and a small library of spirocyclic oxindoles.

An uncommon multicomponent reaction involving nucleophilic heterocyclic carbenes: facile synthesis of fully substituted cyclopentanones

An unprecedented three component reaction involving arylidene oxazolone, enal and NHC, leading to the synthesis of fully substituted cyclopentanone derivatives with three contiguous stereocenters, is reported.

Substituted spirooxindole derivatives as potent anticancer agents through inhibition of phosphodiesterase 1

Spirooxindole is a promising chemo therapeutic agent. Possible targets include cancers of the liver, prostate, lung, stomach, colon, and breast. Here, we demonstrate a one-pot three-component reaction via a [3 + 2] cycloaddition/ring contraction sequence of a dipolarophile (activated alkene) with in situ-generated azomethine ylide (1,3-dipoles) without the use of any catalyst. The reaction provides efficient access to synthetically useful and biologically important spirooxindoles in high yield (69–94%) with high diastereoselectivity. The synthesized compounds were subjected to cytotoxicity evaluation using colorectal cancer (HCT-116), hepatocellular carcinoma (HepG2), and prostate cancer (PC-3) cells. Compounds 4i, 4j, and 4k showed potent cytotoxic activity and high selectivity against HCT-116 cells when compared to cisplatin. Meanwhile compound 4d retained high cytotoxic activity and selectivity against HepG2 and PC-3 cells in comparison to cisplatin. The mechanism of compound 4d was further studied using phosphodiesterase 1 enzyme and showed 74.2% inhibitory activity. A possible binding mode for compound 4d to PDE-1 was investigated by molecular modeling using OpenEye software. Pose predictions for the active compounds were demonstrated by ROCS alignments. Compound 4d has a special geometry and differs from other active compounds.

Spirooxindole is a promising chemo therapeutic agent. Possible targets include cancers of the liver, prostate, lung, stomach, colon, and breast.

Leucine rich repeat kinase 2 (LRRK2) inhibitors based on indolinone scaffold: Potential pro-neurogenic agents

Leucine-rich repeat kinase 2 (LRRK2) is one of the most pursued targets for Parkinson's disease (PD) therapy. Moreover, it has recently described its role in regulating Wnt signaling and thus, it may be involved in adult neurogenesis. This new hypothesis could give rise to double disease-modifying agents firstly by the benefits of inhibiting LRRK2 and secondly by promoting adult neurogenesis. Herein we report, the design, synthesis, biological evaluation, SAR and potential binding mode of indoline-like LRRK2 inhibitors and their preliminary neurogenic effect in neural precursor cells isolated from adult mice ventricular-subventricular zone. These results open new therapeutic horizons for the use of LRRK2 inhibitors as neuroregenerative agents. Moreover, the indolinone derivatives here prepared, inhibitors of the kinase activity of LRRK2, may be considered as pharmacological probes to study the potential neuroregeneration of the damaged brain.

Synthesis of 2,3′-spirobi[indolin]-2-ones enabled by a tandem nucleophilic benzylation/C(sp2)–N cross-coupling reaction sequence

This study provides an efficient strategy for the construction of spiro[pyrrolidin-3,2′-oxindoles] and represents a new perspective for the synthesis of spirocyclic oxindoles.

An enantioselective synthesis of spiro-oxindole-based 3,4-dihydropyrroles via a Michael/cyclization cascade of 3-aminooxindoles with 2-enoylpyridines

This work provides a highly stereoselective route to access spiro[pyrrolidin-3,2′-oxindoles] and represents a new perspective for the synthesis of spirocyclic oxindoles.

NHC-catalyzed [4 + 2] annulation of 2-bromo-2-enals with acylhydrazones: enantioselective synthesis of δ-lactams

An asymmetric assembly of δ-lactams was realized via the NHC-catalyzed formal [4 + 2] annulation of acylhydrazones and 2-bromo-2-enals bearing γ-H.

N-Heterocyclic carbene-catalyzed [3 + 2] annulation of bromoenals with 3-aminooxindoles: highly enantioselective synthesis of spirocyclic oxindolo-γ-lactams

The chiral N-heterocyclic carbene-catalyzed [3 + 2] annulation of α-bromoenals and 3-aminooxindoles was developed, giving spirocyclic oxindolo-γ-lactams in good yields with high diastereo- and enantioselectivities.

Organocatalytic enantio- and diastereoselective synthesis of 3,5-disubstituted prolines

The asymmetric synthesis of substituted pyrrolidines has been accomplished using a novel organocatalytic cyclization reaction promoted by aCinchonaalkaloid base primary amine.

Recent advances in employing homoenolates generated by N-heterocyclic carbene (NHC) catalysis in carbon-carbon bond-forming reactions

The use of NHCs for generating homoenolate species has gained widespread popularity in recent years. A number of highly stereoselective processes of NHC-homoenolates have emerged. Homoenolate reactions have also been employed as key steps in the total synthesis of a number of natural products. The use of compatible co-catalysts, improved NHC-catalyst design and the use of novel precursors for homoenolate generation are among the major developments in this area that were disclosed recently. This tutorial review organises and presents the advancements in this rapidly growing area of catalysis and in the process updates a previous account published in 2011 in this journal.