Selective C sp 2CspBond Cleavage: The Nitrogenation of Alkynes to Amides

Palladium-Catalyzed Cascade Carbonylation to α,β-Unsaturated Piperidones via Selective Cleavage of Carbon-Carbon Triple Bonds

A direct and selective synthesis of α,β-unsaturated piperidones by a new palladium-catalyzed cascade carbonylation is described. In the presented protocol, easily available propargylic alcohols react with aliphatic amines to provide a broad variety of interesting heterocycles. Key to the success of this transformation is a remarkable catalytic cleavage of the present carbon-carbon triple bond by using a specific catalyst with 2-diphenylphosphinopyridine as ligand and appropriate reaction conditions. Mechanistic studies and control experiments revealed branched unsaturated acid 11 as crucial intermediate.

Silver-Catalyzed Stereoselective Aminosulfonylation of Alkynes

A silver-catalyzed intermolecular aminosulfonylation of terminal alkynes with sodium sulfinates and TMSN3 is reported. This three-component reaction proceeds through sequential hydroazidation of the terminal alkyne and addition of a sulfonyl radical to the resultant vinyl azide. The method enables the stereoselective synthesis of a wide range of β-sulfonyl enamines without electron-withdrawing groups on the nitrogen atom. These enamines are found to be suitable for a variety of further transformations.

Metal-Catalysed Azidation of Organic Molecules

The azide moiety is a desirable functionality in organic molecules, useful in a variety of transformations such as olefin aziridination, C-H bond amination, isocyanate synthesis, the Staudinger reaction and the formation of azo compounds. To harness the versatility of the azide functionality fully it is important that these compounds be easy to prepare, in a clean and cost-effective manner. Conventional (non-catalysed) methods to synthesise azides generally require quite harsh reaction conditions that are often not tolerant of functional groups. In the last decade, several metal-catalysed azidations have been developed in attempts to circumvent this problem. These methods are generally faster, cleaner and more functional-group-tolerant than conventional methods to prepare azides, and can sometimes even be conveniently combined with one-pot follow-up transformations of the installed azide moiety. This review highlights metal-catalysed approaches to azide synthesis, with a focus on the substrate scopes and mechanisms, as well as on advantages and disadvantages of the methods. Overall, metal-catalysed azidation reactions provide shorter routes to a variety of potentially useful organic molecules containing the azide moiety.

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.

Meeting the challenge of intermolecular gold(I)-catalyzed cycloadditions of alkynes and allenes

The development of gold(I)-catalyzed intermolecular carbo- and hetero-cycloadditions of alkynes and allenes has been more challenging than their intramolecular counterparts. Here we review, with a mechanistic perspective, the most fundamental intermolecular cycloadditions of alkynes and allenes with alkenes.