Divergent Construction of Diverse Scaffolds through Catalyst-Controlled C-H Activation Cascades of Quinazolinones and Cyclopropenones

Palladium-Catalyzed Regioselective [3 + 2] Annulation with N-Allenamides at the Proximal C═C Bond: Synthesis of γ-Amino-α'-methylenecyclopentenones

A palladium-catalyzed [3 + 2] cycloaddition of cyclopropenones with N-allenamides has been developed. This methodology facilitates the synthesis of γ-amino-α'-methylenecyclopentenones in moderate to excellent yields with good regioselectivity and compatibility with various functional groups. The employment of N-allenamides as versatile 2C synthons enables simultaneous incorporation of both a nitrogen atom and a methylene group into cyclopentenones. Furthermore, this approach exhibits reverse regioselectivity when compared to general allenes. Density functional theory calculations successfully elucidated the origin of the observed regioselectivity.

Ag-Catalyzed cross-dehydrogenative-coupling for the synthesis of 1,4-dioxan-2-yl substituted quinazoline hybrids in an aqueous medium

We herein developed an effective approach for the construction of 2- or 4-(1,4-dioxan-2-yl) substituted quinazolines under mild conditions. A silver-K2S2O8 catalyzed direct CDC reaction between quinazolines and 1,4-dioxane for the synthesis of a series of 2- or 4-(1,4-dioxan-2-yl) substituted quinazoline hybrids is reported. The reaction proceeded well in water under mild conditions and showed a broad substrate scope and good functional group compatibility.

Ag-Catalyzed Selective C-C Bond Activation of Cyclopropenones to Access α-Alkylidene Lactones

A novel Ag-catalyzed ring opening of unsymmetric cyclopropenones for the stereoselective synthesis of a diverse range of α-alkylidene lactones has been developed. In this protocol, two different C-C(O) bonds were distinguished, demonstrating selective C-C bond activation. This reaction features a wide substrate scope, good functional group compatibility, and high atom economy, providing a versatile and general approach to the construction of α-alkylidene lactones.

Visible-light-induced three-component reactions of α-diazoesters, quinazolinones and cyclic ethers toward quinazoline-based hybrids

An effective approach for the construction of 4-short-chain ether attached carbonyl group-substituted quinazolines was developed. Visible-light-induced three-component reactions of α-diazoesters, quinazolinones, and cyclic ethers, with a broad substrate scope and excellent functional group tolerance, under extremely mild conditions without the need for any additional additives and catalysts, selectively led to quinazoline-based hybrids in good to excellent yields. The synthesized hybrids, which are a conglomeration of a quinazoline, a short-chain ether, and a carbonyl group in one molecular skeleton, have potential for application in the development of new drugs or drug candidates.

Pd-Catalyzed Three-Component Coupling of Cyclopropenones via Sequential C-C Bond Activation and Allylation

A novel Pd-catalyzed three-component domino reaction for the stereoselective synthesis of highly functionalized allyl cinnamates has been developed. In this protocol, a sequential process of C-C bond activation and intermolecular allylic substitution was well-organized. The key for this transformation is the in situ generated hydrolysis product of cyclopropenone, which triggered a new reaction with vinylethylene carbonates. The reaction mechanism was investigated, demonstrating the high stereoselectivity and excellent atomic economy in this process.

Rh(III)-Catalyzed Double C-H Functionalization of Indoles with Cyclopropenones via Sequential C-H/C-C/C-H Bond Activation

An unprecedented Rh(III)-catalyzed double C-H functionalization of indoles with cyclopropenones via sequential C-H/C-C/C-H bond activation has been developed. This procedure represents the first example for assembling of cyclopenta[b]indoles utilizing cyclopropenones as 3C synthons. This powerful approach shows excellent chemo- and regioselectivity, wide functional group tolerance, and good reaction yields.

Ir(III)-Catalyzed Dual C-H Activation of 2-Aryl Phthalazinediones and 3-Aryl-2H-benzo[e][1,2,4]thiadiazine-1,1-dioxides for the Construction of Spiro-Fused Cyclic Frameworks

An Ir(III)-catalyzed double C-H activation strategy has been developed for the synthesis of highly rigid spiro frameworks by means of ortho-functionalization of 2-aryl phthalazinediones and 2,3-diphenylcycloprop-2-en-1-ones using the Ir(III)/AgSbF₆ catalytic system. Similarly, 3-aryl-2H-benzo[e][1,2,4]thiadiazine-1,1-dioxides undergo smooth cyclization with 2,3-diphenylcycloprop-2-en-1-ones to afford a diverse range of spiro compounds in good yields with excellent selectivity. Additionally, 2-arylindazoles provide the corresponding chalcone derivatives under similar reaction conditions.

Tandem C-C/C-N Bond Formation via Rh(III)-Catalyzed α-Fluoroalkenylation and Sequential Annulation of 2-Arylquinazolinones and gem-Difluorostyrenes

An efficient method of Rh(III)-catalyzed coupling reaction between 2-arylquinazolinones and gem-difluorostyrenes has been developed. In this work, two diverse structures of monofluoroalkenes and isoindolo[1,2-b]quinazolin-10(12H)-one derivatives were respectively synthesized by controlling the amount of additives (Ca(OH)₂ and AgNTf₂) to achieve controlled stepwise breaking of the C-F bonds of gem-difluorostyrenes. This reaction has the characteristics of a wide range of substrates and good functional group tolerance. Meanwhile, several control experiments were conducted and a plausible mechanism was proposed.

Heterocycles from cyclopropenones

Great attention has been paid to cyclopropenones as they are present in many natural sources. Various synthesized cyclopropenone derivatives also show a wide range of biological activities. The cyclopropenone derivatives undergo a variety of reactions such as ring-opening reactions, isomerization reactions, C-C coupling reactions, C-H activation, cycloaddition reactions, thermal and photo-irradiation reactions, and acid-base-catalyzed reactions under the influence of various chemical reagents (electrophiles, nucleophiles, radicals, and organometallics) and external forces (heat and light). Many previous reviews have dealt with the chemistry and reactions of cyclopropenones. However and to the best of our knowledge, the utility of cyclopropenones in the synthesis of heterocycles has not been reported before. Therefore, it would be interesting to shed light on this new topic. The present review article provides, for the first time, a comprehensive compilation of synthetic methods for the synthesis of various heterocyclic ring systems, as a significant family in the field of organic chemistry.

Palladium-Catalyzed Synthesis of Functionalized Indoles by Acylation/Allylation of 2-Alkynylanilines with Three-Membered Rings

Palladium-catalyzed synthesis of 3-acyl and -allyl indoles has been realized by merging nucleophilic cyclization of ortho-alkynylanilines with ring opening of three-membered rings such as cyclopropenones and gem-difluorinated cyclopropanes. These functionalized indoles were obtained in moderate to high yields with high stereoselectivity in both cases. This protocol provides an alternative method toward functionalized indoles under mild and redox-neutral conditions.