TMSCl-Mediated Synthesis of α,β-Unsaturated Amides via C–C Bond Cleavage and C–N Bond Formation of Propargyl Alcohols with Trimethylsilyl Azide

Amidation of Enones via Beckmann Rearrangement

The Beckmann reaction is one of the most atom-economical methods for the preparation of amides from ketones. Unlike ketones, the multiple competing reactivities of enones as well as the requirement of demanding reaction conditions for in situ generation of oximes have severely impacted the application of this reaction for the preparation of α,β-unsaturated amides. Herein, we describe the first chemoselective method for the direct conversion of enones to the corresponding α,β-unsaturated amides using N-Boc-O-tosylhydroxylamine.

Manganese(I) Catalyzed α-Alkenylation of Amides Using Alcohols with Liberation of Hydrogen and Water

Herein, unprecedented manganese-catalyzed direct α-alkenylation of amides using alcohols is reported. Aryl amides are reacted with diverse primary alcohols, which provided the α,β-unsaturated amides in moderate to good yields with excellent selectivity. Mechanistic studies indicate that Mn(I) catalyst oxidizes the alcohols to their corresponding aldehydes and also plays an important role in efficient C═C bond formation through aldol condensation. This selective olefination is facilitated by metal-ligand cooperation by the aromatization-dearomatization process operating in the catalytic system. Biorenewable alcohols are used as alkenylation reagents for the challenging α-alkenylation of amides with the highly abundant base metal manganese as a catalyst, which results in water and dihydrogen as the only byproduct, making this catalytic transformation attractive, sustainable, and environmentally benign.

Stereoselective Formal Hydroamidation of Si-Substituted Arylacetylenes with DIBAL-H and Isocyanates: Synthesis of (E)- and (Z)-α-Silyl-α,β-unsaturated Amides

An efficient and stereoselective method for the synthesis of (E)- and (Z)-α-silyl-α,β-unsaturated amides and its synthetic applications are presented herein. The solvent-controlled hydroaluminations of Si-substituted alkynes with DIBAL-H generate diastereomerically enriched alkenylaluminum reagents that are directly reacted with isocyanates at ambient temperature to afford α-silyl-α,β-unsaturated amides in high yields with retained stereoselectivity. In particular, this process enables the synthesis of a broad range of (E)-α-silyl-α,β-unsaturated amides, which are the less studied isomers. The synthetic utility of this method is highlighted by its short reaction time, ease of purification, easily accessible substrates and reagents, gram-scale synthesis, and the further transformations of C-Si bonds into C-H, C-X, and C-C bonds.

Synthesis of 1,6-Dihydropyridine-3-carbonitrile Derivatives via Lewis Acid-Catalyzed Annulation of Propargylic Alcohols with (E)-3-Amino-3-phenylacrylonitriles

A novel Lewis acid-catalyzed, highly efficient, practical, and atom-economical protocol for the synthesis of functionalized 1,2-dihydropyridine-3-carbonitrile derivatives in the presence of Bi(OTf)₃ (10 mol %) in tetrahydrofuran (2.0 mL) at 80 °C for 8 h in air is described, starting from readily accessed propargylic alcohols and (E)-3-amino-3-phenylacrylonitriles. This cycloaddition protocol, which is scalable and proceeds under mild conditions, is amenable to the gram-scale construction of valuable 1,2-dihydropyridine-3-carbonitriles. Furthermore, the good functional group compatibility and broad scope of this strategy were demonstrated by a broad range of propargylic alcohols and (E)-3-amino-3-phenylacrylonitriles, with yields ranging from 34 to 96%.

Silver Trifluoromethanesulfonate-Catalyzed Annulation of Propargylic Alcohols with 3-Methyleneisoindolin-1-one

A silver-catalyzed formal [3 + 3] annulation of 3-methyleneisoindolin-1-one with alkynol for the synthesis of 1,5-dihydroindolizin-3(2H)-one derivatives is disclosed. The protocol allows practical synthesis of N-heterocyclic scaffolds with a broad scope of functional groups and could be efficiently scaled up to gram scale, which incarnates a potential application of this methodology. In addition, a range of chlorine anion substitution of alkenes can be constructed by adjusting the structure of the alkynol substrates with the use of TMSCl.

Zn(OTf)2-Catalyzed Formal [3 + 3] Cascade Annulation of Propargylic Alcohols with 2-Aminochromones: Accessing the Chromeno[2,3-b]pyridines

A Zn(OTf)₂-catalyzed formal [3 + 3] cascade annulation strategy for the synthesis of functionalized chromeno[2,3-b]pyridines has been developed using propargylic alcohols and 2-aminochromones as the substrates. The protocol provides a convenient and atom-economical method of accessing a broad range of chromeno[2,3-b]pyridine derivatives in excellent yields with good functional-group tolerance. The method is also effective on the gram scale, which highlights the inherent practicality of this synthetic transformation.

Synthesis of 2-substituted 3-chlorobenzofurans via TMSCl-mediated nucleophilic annulation of isatin-derived propargylic alcohols

A TMSCl-mediated cascade annulation of isatin-derived propargylic alcohols for the synthesis of 2-substituted 3-chlorobenzofurans is now reported. Mechanistic investigations showed that this proceeded through a sequential Meyer-Schuster rearrangement/nucleophilic addition/intramolecular annulation. TMSCl not only acts as a promoter, but also acts as a chlorine source in this protocol.

An efficient approach to 4-chloro quinolines via TMSCl-mediated cascade cyclization of ortho-propynol phenyl azides

A novel and efficient strategy for the synthesis of 4-chloro quinolines via the TMSCl-mediated cascade cyclization of easily prepared ortho-propynol phenyl azides is developed.

Titanium-Promoted Cross-Coupling for the Selective Synthesis of Polysubstituted, Conjugated Amides

α,β-Unsaturated amides are important building blocks and are key structural elements in a number of biologically active natural products. Despite their importance and prevalence, few methods exist to prepare conjugated amides directly and modularly. To address this gap, a titanium-promoted coupling of alkynes and isocyanates has been developed. The method is highly stereoselective, producing only the E isomer with good chemoselectivity and regioselectivity (>95/5), for unsymmetrical internal alkynes that contain a steric bias. The reactive titanacyclopentene intermediate formed from the coupling of the alkyne and isocyanate was additionally reacted with various electrophiles to access tetrasubstituted enamides.

Recent advances in the tandem reaction of azides with alkynes or alkynols

Over the past few decades, the development of versatile methodologies to employ azides as aminating agents for the formation of nitrogen-containing compounds has attracted significant attention in synthetic chemistry.

Splitting a Substrate into Three Parts: Gold-Catalyzed Nitrogenation of Alkynes by C-C and C≡C Bond Cleavage

A gold-catalyzed nitrogenation of alkynes for the synthesis of carbamides and amino tetrazoles through C-C and C≡C bond cleavages is described. A diverse set of functionalized carbamide and amino tetrazole derivatives were selectively constructed under mild conditions. The chemoselectivity can be easily switched by the selection of the acid additives. The reaction is characterized by its broad substrate scope, direct construction of high value products, easy operation under air, and mild conditions at room temperature. This chemistry provides a way to transform alkynes by splitting the substrate into three parts.

Synthesis of α,β-Unsaturated N-Sulfonyl Imides through Zinc-Catalyzed Intermolecular Oxidation of N-Sulfonyl Ynamides

A novel zinc-catalyzed intermolecular oxidation of N-sulfonyl ynamides has been developed. A variety of functionalized α,β-unsaturated N-sulfonyl imides are readily accessed by utilizing this approach, thus providing a viable alternative to synthetically useful α,β-unsaturated imides. Importantly, the reaction is proposed to proceed by a vinyligous E2-type elimination pathway, but not metal carbene pathway.

An efficient three-component synthesis of coumarin-3-carbamides by use of Ni–NiO nanoparticles as magnetically separable catalyst

An efficient and ecofriendly synthesis of coumarin-3-carbamides has been developed by a three-component reaction of 2-hydroxybenzaldehydes, aliphatic amines (p-/s-) and diethyl malonate using Ni–NiO nanoparticles as catalyst.

A Ce(OTf)3/PyBox catalyzed enantioselective Hosomi–Sakurai reaction of aldehydes with allyltrimethylsilane

An approach to the efficient synthesis of enantioselective homoallylic alcohols has been developed by the use of a catalytic amount of a cerium/PyBox complex.

A combination of trimethylsilyl chloride and hydrous natural montmorillonite clay: an efficient solid acid catalyst for the azidation of benzylic and allylic alcohols with trimethylsilyl azide

We present a new procedure to convert in situ natural montmorillonite clay into a partially acidified one using a catalytic amount of trimethylsilyl chloride and trace water.