Ruthenium-Catalyzed Enantioselective Intramolecular Propargylation of Thiophenes with Propargylic Alcohols

Transition Metal Vinylidene- and Allenylidene-Mediated Catalysis in Organic Synthesis

With their mechanistic novelty and various modalities of reactivity, transition metal unsaturated carbene (alkenylidene) complexes have emerged as versatile intermediates for new reaction discovery. In particular, the past decade has witnessed remarkable advances in the chemistry of metal vinylidenes and allenylidenes, leading to the evolution of a diverse array of new catalytic transformations that are mechanistically distinct from those developed in the previous two decades. This review aims to provide a survey of the recent achievements in the development of organic reactions that make use of transition metal alkenylidenes as catalytic intermediates and their applications to organic synthesis.

Scope and advances in the catalytic propargylic substitution reaction

Nucleophilic displacement of the propargylic alcohol is one of the sought-after methods in the current scenario. The highly nucleophilic alkyne functional moiety along with its considerably acidic terminal hydrogen atom allows the propargylic unit to play a crucial role in organic synthesis by offering a handle for further synthetic transformations. Until 2000, the most fundamental propargylic substitution reaction was the Nicolas reaction, a multi-step transformation, developed in 1972, which involved cobalt as a stoichiometric promoter. Therefore, the direct catalytic substitution of propargylic alcohols was a highly desirable method for development. The pioneering work on the Ru-catalyzed propargylic substitution reaction in 2000 encouraged many researchers to develop several novel catalytic propargylic substitution reactions, which have made rapid progress since then. The purpose of this review is to emphasise the involvement of diverse types of Lewis acid, transition metal and Brønsted acid catalysts in the propargylic substitution reaction and provide an updated summary of the recent developments in this field. The selected examples presented here are the most significant and relevant ones and we believe that this will help the readers to comprehend the scope of the propargylic substitution reaction with diverse types of catalysts and will envisage the scientific community for the future developments in this field.

Direct nucleophilic displacement of the alpha-hydroxy of the propargylic alcohol is one of the sought-after methods in the current scenario. An updated summary of the recent developments in this field is presented here.

Ruthenium-catalyzed synthesis of 2,3-cyclo[3]dendralenes and complex polycycles from propargyl alcohols

Ruthenium-catalyzed cascade transformations for the synthesis of 2,3-cyclo[3]dendralenes and multicomponent processes based thereon to generate complex polycycles are presented. The combination of allylation-cyclization sequences with diene-transmissive Diels-Alder reactions allows the rapid and selective construction of natural-product-like motifs from easily accessible starting materials in a one-pot process and provides a new method to access potential drug candidates.

Highly diastereo- and enantioselective copper-catalyzed propargylic alkylation of acyclic ketone enamines for the construction of two vicinal stereocenters

Highly diastereo-/enantioselective Cu-catalyzed propargylic alkylation of acyclic ketone enamines to form vicinal tertiary stereocenters was developed using a chiral tridentate ketimine P,N,N-ligand.

Copper-catalyzed enantioselective propargylic substitution of propargylic acetates with enamines

With the use of chiral tridentate P,N,N ligand, copper-catalyzed enantioselective propargylic substitution of propargylic acetates with enamines has been achieved, giving the corresponding propargylic ketones in high yields and with excellent enantioselectivities.