Palladium/Brønsted Acid Catalysis for Hydrofunctionalizations of Alkynes: From Tsuji‐Trost Allylations to Stereoselective Methodologies

Abstract

Alkynes are one of the most abundant feedstocks for chemical transformations. By merging palladium and Brønsted acid catalysts, they are converted into reactive allylmetal species, which become suitable for Tsuji‐Trost functionalizations with complete atom‐economy. This approach, which overcomes the limitations of traditional methods that suffer from the formation of over‐stoichiometric amounts of by‐products, has been disclosed for developing new C−C and C−Het bond forming methodologies. Within this review, we aim to survey the latest advancements in this area including applications in polymer chemistry, deuterium‐labeling and stereoselective catalysis.

Asymmetric formal sp2-hydrocarbonations of dienes and alkynes via palladium hydride catalysis

“…A general mechanism for transition metal-catalyzed asymmetric hydrofunctionalizations of alkynes with outer-sphere nucleophiles involves the sequential conversion of alkyne into allene intermediate, hydrometallation of allene to generate thermodynamically stable ƞ 3 -allylmetal species and final allylic substitution 1 , 73 . Following the seminal work by Yamamoto 74 – 76 , progress has been made on this area under palladium catalysis based on aforementioned mechanistic proposal.…”

Recent Advances in Pd‐Catalyzed Reactions Involving the “On‐Water” Mechanism†

“…[ 19‐24 ] It is commonly known that Pd‐catalyzed reactions currently stand as highly reliable methods for the construction of carbo‐ and heterocyclic complex molecules. [ 25‐28 ] In recent years, extensive efforts have been devoted to the development of Pd‐catalyzed aqueous reactions, [ 29‐32 ] in some cases, reactions were even more efficient than in organic solvents; although transition metal‐mediated reactions have long been thought to be incompatible with water.…”

Remote Functionalization by Pd-Catalyzed Isomerization of Alkynyl Alcohols

“…The Trost and Lu groups concurrently disclosed highly stereoselective Pd-, Ru-, and Ir-based systems for the isomerization of α,β-ynones, α,β-ynoic esters, and α,β-ynoic amides to the corresponding α,β,γ,δ-unsaturated carbonyl derivatives. , In comparison, Yamamoto and Hayashi independently established that complex stereoisomeric mixtures are usually obtained in the absence of a stabilizing functional group. , More recently, Zhang and co-workers showed that aryl-alkynes and sulfonyl-protected ynamides underwent yne-to-diene isomerization with high levels of stereocontrol under gold catalysis in the presence of an elaborated Buchwald-type monophosphine ligand . While the ruthenium systems employed by Ikawa for the isomerization of propargyl (silyl)­ethers and propargyl ethers delivered mixtures of geometrical isomers, Maestri showed that propargyl amines were isomerized with high levels of stereocontrol using simple palladium precursors and a catalytic amount of benzoic acid . The isomerization of primary and secondary propargylic alcohols into α,β-unsaturated aldehydes and ketones has been achieved with several Rh, Ru, Ir, and Pd precursors under thermal conditions .…”