Enantioselective synthesis of tricyclic oxoquinolines via NHC-catalyzed Michael-aldol-lactamization-dehydration cascade

The enantioselective synthesis of tricyclic oxoquinolines via NHC-catalyzed cascade reaction of enals with malonates bearing a 2-aminophenyl group is reported. The chiral α,β-unsaturated acylazoliums underwent a smooth Michael-aldol-lactamization-dehydration quadruple cascade with the amino malonate derivative to afford the desired tricyclic products.

Synthesis of γ-Lactams from Acrylamides by Single-Carbon Atom Doping Annulation

A protocol for single-carbon atom doping annulation is reported, which enables the conversion of acrylamides into homologated γ-lactams through the cleavage of two σ-bonds and the formation of four new σ-bonds at the single carbon center. The key strategy is the use of N-heterocyclic carbenes as an atomic carbon equivalent by acting as carbon atom donors through the loss of a 1,2-diimine moiety. Experimental and computational studies reveal that the reaction proceeds through a spirocyclic intermediate, followed by the disassembly of the N-heterocyclic carbene skeleton via proton transfer.

Single-carbon atom transfer to α,β-unsaturated amides from N-heterocyclic carbenes

Single-carbon atom transfer reactions are lacking in organic synthesis, partly because of the absence of atomic carbon sources under standard solution-phase conditions. We report here that N-heterocyclic carbenes can serve as atomic carbon donors through the loss of a 1,2-diimine moiety. This strategy is applicable to single-carbon atom transfer to α,β-unsaturated amides, which can be converted into homologated γ-lactams through the formation of four single bonds to one carbon center in one operation.

One carbon-four new bonds

Stable carbenes deliver a carbon atom to simple amides, producing a range of cyclic compounds.

N-Heterocyclic Carbene-Catalyzed Aza-Michael-Mannich-Lactamization Cascade for the Enantioselective Synthesis of Pyrazoloquinolin-3-ones

The enantioselective synthesis of functionalized pyrazoloquinolin-3-ones via N-heterocyclic carbene-catalyzed cascade reaction of α-bromoenals with 2-aminoaryl N-tosyl hydrazones is reported. The in situ-generated α,β-unsaturated acylazoliums underwent an aza-Michael-Mannich-lactamization sequence to afford the tricyclic products bearing three contiguous stereocenters, including a sterically demanding quaternary stereocenter with high enantioselectivity. The unprotected amine-triggered aza-Michael pathway over the competing amidation pathway is noteworthy.

Sequential One-Pot Carbene-Catalyzed Intramolecular Stetter Reaction and Acid-Mediated Condensation: Access to Heteroatom Analogues of π-Extended Polyaromatic Hydrocarbons

In this Letter, we disclose a simple and effective method to access a variety of phenanthro[9,10-b]furan and 1H-dibenzo[e,g]indole derivatives based on the design of a carbene-catalyzed intramolecular Stetter reaction followed by a Paal-Knorr reaction in one-pot. These compounds are a class of π-extended polycyclic aromatic hydrocarbon (PAH) derivatives containing an oxygen/nitrogen atom. The practical utility of the developed transformation was demonstrated on the gram scales and postsynthetic transformations thereof.

N-Heterocyclic Carbene-Catalyzed Umpolung of Cyclopent-4-ene-1,3-diones for Activated Olefin-Isatin Cross-Coupling

N-Heterocyclic carbene (NHC)-catalyzed umpolung of cyclopent-4-ene-1,3-diones that proceeds via the generation of nucleophilic deoxy-Breslow intermediates is presented. The carbene generated from a commercially available thiazolium salt catalyzed the cross-coupling between cyclopent-4-ene-1,3-diones and isatins to furnish the functionalized oxindoles in moderate to good yields with good functional group compatibility. The key deoxy-Breslow intermediates were isolated and characterized by X-ray analysis. Detailed mechanistic studies are also presented.

Non-Stabilized Vinyl Anion Equivalents from Styrenes by N-Heterocyclic Carbene Catalysis and Its Use in Catalytic Nucleophilic Aromatic Substitution

A protocol for the catalytic nucleophilic activation of unactivated styrenes is reported, which enables the generation of a non-stabilized alkenyl anion equivalent as a transient intermediate. In the reaction, N-heterocyclic carbenes add across styrenes to generate ylide intermediates, which can then be used in intramolecular nucleophilic aromatic substitution reactions of aryl fluorides, chlorides, and methyl ethers. The method allows for straightforward access to complex polyaromatic compounds.

NHC Catalysis for Umpolung Pyridinium Alkylation via Deoxy‐Breslow Intermediates

Umpolung N‐heterocyclic carbene (NHC) catalysis of non‐aldehyde substrates offers new pathways for C−C bond formation, but has proven challenging to develop in terms of viable substrate classes. Here, we demonstrate that pyridinium ions can undergo NHC addition and subsequent intramolecular C−C bond formation through a deoxy‐Breslow intermediate. The alkylation demonstrates, for the first time, that deoxy‐Breslow intermediates are viable for catalytic umpolung of areniums.

NHC Catalysis for Umpolung Pyridinium Alkylation via Deoxy-Breslow Intermediates

Umpolung N-heterocyclic carbene (NHC) catalysis of non-aldehyde substrates offers new pathways for C-C bond formation, but has proven challenging to develop in terms of viable substrate classes. Here, we demonstrate that pyridinium ions can undergo NHC addition and subsequent intramolecular C-C bond formation through a deoxy-Breslow intermediate. The alkylation demonstrates, for the first time, that deoxy-Breslow intermediates are viable for catalytic umpolung of areniums.

A DFT study on the mechanism and regioselectivity of NHC-catalyzed double acylation of aromatic 1,2-diketones with α,β-unsaturated ketones

The possible mechanisms and the origin of regioselectivity of the N-heterocyclic carbene (NHC)-catalyzed double acylation reaction of aromatic 1,2-diketones with α,β-unsaturated ketones have been theoretically studied using density functional theory.

Enantioselective Rauhut-Currier Reaction with β-Substituted Acrylamides Catalyzed by N-Heterocyclic Carbenes

β-Substituted acrylamides have low electrophilicity and are yet to be exploited in the enantioselective Rauhut-Currier reaction. By exploiting electron-withdrawing protection of the amide and moderate nucleophilicity N-heterocyclic carbenes, such substrates have been converted to enantioenriched quinolones. The reaction proceeds with complete diastereoselectivity, good yield, and modest enantioselectivity. Derivatizations are reported, as are computational studies, supporting decreased amide bond character with electron-withdrawing protection of the nitrogen.

N-Heterocyclic Carbene-Catalyzed Truce-Smiles Rearrangement of N-Arylacrylamides via the Cleavage of Unactivated C(aryl)-N Bonds

We report on the N-heterocyclic carbene (NHC)-catalyzed Truce-Smiles rearrangement of aniline derivatives, in which an unactivated C(aryl)-N bond is cleaved, leading to the formation of a new C(aryl)-C bond. The key to the success of this reaction is the utilization of a highly nucleophilic NHC, which enables the formation of a highly nucleophilic ylide intermediate that is generated from an α,β-unsaturated amide.

Theoretical study of the NHC-catalyzed C–S bond cleavage and reconstruction reaction: mechanism, stereoselectivity, and role of catalysts

The mechanism of the NHC-catalyzed C–S bond activation reaction has been theoretically studied and ELF analysis along with IRC results shows that the NHC promotes the cleavage of the C–S bond via an SN2 process.

Organocatalytic Name Reactions Enabled by NHCs

Giving reactions the names of their discoverers is an extraordinary tradition of organic chemistry. Nowadays, this phenomenon is much rarer, although already named historical reactions are still often developed. This is also true in the case of a broad branch of N-heterocyclic carbenes catalysis. NHCs allow many unique synthetic paths, including commonly known name reactions. This article aims to gather this extensive knowledge and compare historical reactions with current developed processes. Furthermore, this review is a great opportunity to highlight some of the unique applications of these procedures in the total synthesis of biologically active compounds. Hence, this concise article may also be a source of knowledge for scientists just starting their adventure with N-heterocyclic carbene chemistry.

N-Heterocyclic carbene (NHC) organocatalysis using aliphatic aldehydes

Recent advances are presented in NHC catalysis employing aliphatic aldehydes as substrates for the generation of various carbene-bound intermediates and subsequent interception with electrophiles/nucleophiles.