"Alkene-to-Alkene" Difunctionalization of Enaminones for the Synthesis of Polyfunctionalized Alkenes by Transition-Metal-Free C-H and C-N Bond Transformation

Three-Component 1,3-Difunctionalization of Carbonyl Ylides with Water and Azadienes for the Synthesis of Dihydroisobenzofurans

Multicomponent reactions are an efficient and widely employed synthetic strategy, known for their capability to rapidly and effectively construct complex molecular architectures from multiple starting materials. This work presents a chemo- and diastereoselective three-component reaction for the 1,3-difunctionalization of transient carbonyl ylides with H2O and azadienes, facilitated by the synergistic catalysis of Rh2(OAc)4 and phosphoric acid. This strategy provides an efficient protocol for the synthesis of highly functionalized dihydroisobenzofurans in high yields (up to 94%) and good diastereoselectivities (up to 91:9 dr). Additionally, subsequent transformations with nucleophiles enable the synthesis of structurally diverse compounds with enhanced diastereoselectivities (dr >95:5).

Water-Controlled Geminal Hydroxyphosphinoylation and Diphosphinoylation of Enaminones with H-Phosphine Oxides

A water-controlled geminal phosphinoylation of enaminones with H-phosphine oxides has been established through AlCl3-mediated C-N bond cleavage in this work, which provides a novel strategy for accessing various hydroxy and diphosphinoyl products 3a and 4a in high yields. The transformation features excellent functional group tolerance, operational simplicity, and high atom economy, and is amenable for phosphinoylation of complex molecule skeletons. Preliminary mechanism studies suggest the conversion from 3a to 4a involve the elimination of hydroxyl group, and water and temperature plays a critical role in influencing the reaction pathway and product selectivity. This research provides significant value to the geminal functionalization of enaminones.

Tunable Synthesis of 4-Acyl- and 4-Formyl Pyrroles by Rhodium-Catalyzed Ring-Expansion of Azirines with Enaminones

A rhodium-catalyzed annulation of 2H-azirines with enaminones is presented. This protocol affords a convenient approach to the diversity-oriented synthesis of 4-acyl- and 4-formyl pyrroles with good functional group tolerance. The utility of this reaction has been demonstrated by scale-up preparation, late-stage modification of natural molecules, and synthesis of diverse derivatives.

Assembly of Diverse Allenes via Activator-Free Palladium-Catalyzed Regioselective γ-Arylation of Propargylamines with Boronic Acids

Controlling the reaction selectivity to achieve a precision synthesis is a constant concern for chemists. Here, we report a palladium-catalyzed deaminative coupling of propargylamines with arylboronic acids to generate allene skeletons. Importantly, this approach allows the regioselective γ-arylation of unactivated propargyl tertiary amines to access various allenes in the absence of amino-activating reagents. We present a wide range of propargylamines and boronic acids and demonstrate the synthetic application of the target products to construct valuable compounds.

Metal-free hydrodifunctionalization of enaminones for the synthesis of ketomethylene-functionalized phosphoryl alcohols

Reported here is a set of three-component reactions of enaminones with diaryl phosphine oxides and water for the synthesis of ketomethylene-functionalized gem-phosphoryl alcohols via enaminone hydrodifunctionalization, enabling the cascade construction of new C-P, C-O and C-H bonds. The method displays notable advantages including mild metal-free conditions, a broad application scope and being free of the need to carry out chromatographic purification.

Divergent Synthesis of Enynals and Dihydrobenzo[f]isoquinolines via Deoxyalkynylation of Enaminones Enabled by the Cooperative Action of Tf2O/Pd/Cu

A variety of enynals and dihydrobenzo[f]isoquinolines were effectively synthesized with favorable functional group compatibility via deoxyalkynylation of enaminones enabled by the cooperative action of Tf2O/Pd/Cu. The reaction system demonstrated the ability to be expanded to the deoxyarylation/deoxyaryloxylation of enaminones with arylboronic acids or phenols, facilitating the efficient formation of C-C/C-O bonds and showcasing the practicality and versatility of the methodology.

Cascade [3 + 2] Annulation of 1,3-Dicarbonyl Compounds and Ethyl Secondary Amines for Pyrrole Synthesis via Poly C(sp3)-H Bond Functionalization

The synthesis of polyfunctionalized pyrroles via the cascade reactions of 1,3-dicarbonyl compounds and two molecules of ethyl secondary amines has been realized via simple iodine catalysis in the presence of Dess-Martin periodinane (DMP). The formation of the target pyrrole products involves the formation of one new C-C and two new C-N bonds via the major functionalization of six C(sp3)-H bonds, presenting a highly novel and efficient synthetic protocol toward pyrrole scaffolds.

Synthesis of 6-oxa-Spiro[4.5]decane Derivatives by Merging Ring-Opening of Benzo[c]oxepines and Formal 1,2-Oxygen Migration

A facile one-pot synthetic method has been developed for constructing 6-oxa-spiro[4.5]decane skeletons by merging the ring-opening of benzo[c]oxepines and formal 1,2-oxygen migration reactions. More than 30 examples of the 6-oxa-spiro[4.5]decane derivatives have been synthesized under transition-metal-free conditions.

Iridium-catalyzed reduction of o-hydroxyl phenyl enaminones for the synthesis of propiophenones and their application in 3-methyl chromone synthesis

A method of reducing o-hydroxyphenyl enaminones with silane as the reductant to provide o-hydroxyl propiophenones has been achieved with iridium catalysis. The reduction reactions were found to proceed via the assistance of the hydroxyl group in the phenyl ring. In addition, the o-hydroxyl propiophenone products were used for the easy synthesis of 3-methyl chromones by directly incorporating N,N-dimethyl formamide dimethyl acetal (DMF-DMA) without using any catalyst.

Photocatalytic Pyridine Synthesis with Enaminones and TMEDA under Metal-Free Conditions

Reported herein is a new photocatalytic annulation for the synthesis of 2,3,4,6-tetrasubstituted pyridines with enaminones and N,N,N',N'-tetramethyl ethylenediamine (TMEDA). The photocatalytic reactions take place without requiring a transition metal reagent and provide products with broad scope. The methyl in TMEDA acts as the carbon source in pyridine ring construction, and BrCF2CO2Et plays the role of the terminal oxidant for free radical quenching.

Rhodium(III)-Catalyzed Coupling of Quinolin-8-carboxaldehydes with CF3-Imidoyl Sulfoxonium Ylides by Chelation-Assisted C(sp2)-H Bond Activation for the Synthesis of Trifluoromethyl-Substituted Enaminones

A rhodium(III)-catalyzed aldehydic C(sp2)-H imidoylmethylation of quinolin-8-carboxaldehydes with CF3-imidoyl sulfoxonium ylides (TFISYs) has been developed for the generation of α-imino ketones, which could be readily tautomerized to enaminones in moderate to excellent yields. In the transformation, TFISYs act as a kind of masked alkenylating reagents for the aldehyde moiety, and the obtained CF3-enaminone products have been successfully converted into other useful trifluoromethyl-substituted heterocycles.

Copper-Catalyzed Three-Component Synthesis of β-Hydroxysulfides from Styrene Oxide, Aryl Iodide, and Carbon Disulfide

A copper-catalyzed three-component coupling reaction of styrene oxide, aryl iodide, and carbon disulfide for the construction of β-hydroxysulfides has been developed. In this process, readily available CS2 was used as the sulfur source to construct C-S bonds for the synthesis of phenyl-β-hydroxysulfides and (benzo[d]thiazol)-β-hydroxysulfides. This process features mild reaction conditions, simple operation, and wide substrate scope (>50 examples).

Transition-Metal-Free C-H Trifluoromethylthiolation of N,N-Disubstituted Enaminones To Access CF3S-Functionalized Enaminones and Their Application in the Synthesis of CF3S-Heteroaryls

The α-C-H trifluoromethylthiolation of N,N-disubstituted enaminones has been achieved with simple and cheap CF3SO2Na as the CF3S source. The reactions were run at mild temperature (0 °C to rt) using POCl3 as the only reducing reagent. The work represents the first example on the synthesis of α-trifluoromethylthio enaminones via direct C-H functionalization. In addition, the resulting CF3S-functionalized enaminones have been proven as useful building blocks in the synthesis of various CF3S-functionalized heteroaromatic compounds by simple annulation reactions.

Oxidative Free-Radical C(sp2)-H Bond Chlorination of Enaminones with LiCl: Access to Highly Functionalized α-Chlorinated Enaminones

An oxidative free-radical C(sp2)-H bond chlorination strategy of enaminones has been developed by using LiCl as a chlorinating reagent and K2S2O8 as an oxidant. This transformation provides a new and straightforward synthetic methodology to afford highly functionalized α-chlorinated enaminones with a Z-configuration in good to excellent yields.

Organic Base-Promoted C-N- and C-O-Coupled Domino Cyclization Strategy: Syntheses of Oxazine-6-ones and 4-Pyrimidinols

Oxazine-6-one and 4-pyrimidinol are two important frameworks in pharmaceutical production. Herein, we disclosed a simple, efficient, inexpensive organic base-promoted and additive-stimulated protocol for the syntheses of variably functionalized oxazine-6-ones and 4-pyrimidinols employing acetonitrile solvent under conventional heating conditions using an oil bath through C-N and C-O coupled domino steps. This simple practicable productive protocol utilizes easily producible cheap precursors, namely, benzimidates or benzamidines, with differently substituted dicyano-olefins, and it comprises step economy, robustness, and moisture insensitive conditions affording high yield that avoids the use of transition-metal catalysts, multistep with multicomponent strategy, and harsh reaction conditions involving hazardous chemicals. This method is scalable into gram-scale production with good yield.

Iodine-Promoted Thioylation and Dicarbonylation of Enaminone α-C Sites: Synthesis of Fully Substituted Thiazoles via C═C Bond Cleavage

A novel iodine-promoted difunctionalization of α-C sites in enaminones was demonstrated as a means of synthesizing a variety of fully substituted thiazoles by constructing C-C(CO), C-S, and C-N bonds. This transformation allows the realization of enaminones as unusual aryl C2 synthons and simultaneously allows the thioylation and dicarbonylation of α-C sites. A preliminary mechanistic study was performed and indicated that the cleavage of C═C bonds in enaminones involves a bicyclization/ring-opening and oxidative coupling sequence.