Straightforward and Efficient Deuteration of Terminal Alkynes with Copper Catalysis

The mild and effective preparation of deuterated organic molecules is an active area of research due to their important applications. Herein, we report an air-stable and easy to access copper(I) complex as catalyst for the deuteration of mono-substituted alkynes. Reactions were carried out in technical solvents and in the presence of air, to obtain excellent deuterium incorporation in a range of functionalised alkynes.

C-H deuteration of organic compounds and potential drug candidates

C-H deuteration has been intricately developed to satisfy the urgent need for site-selectively deuterated organic frameworks. Deuteration has been primarily used to study kinetic isotope effects of reactions but recently its significance in pharmaceutical chemistry has been discovered. Deuterium labelled compounds have stolen the limelight since the inception of the first FDA-approved deuterated drug, for the treatment of chorea-associated Huntington's disease, and their pharmacological importance was realised by chemists, although surprisingly very late. Various approaches were developed to carry out site-selective deuteration. However, the most common and efficient method is hydrogen isotope exchange (HIE). This review summarises deuteration methods of various organic motifs containing C(sp²)-H and C(sp³)-H bonds utilizing C-H bond functionalisation as a key step along with a variety of catalysts, and exemplifies their biological relevance.

Practical approaches to labelling terminal alkynes with deuterium

Base catalysed exchange with sodium hydroxide, calcium oxide or N,N,N,N‐tetramethylguanidine in deuterium oxide is a viable procedure for the preparation of terminally deuterated alkynes for those alkynes stable to strong base. The use of silver perchlorate as a catalyst is an alternative practical option when labelling alkynes which are sensitive to base or contain functionalities which would lead to labelling elsewhere in the molecule. Labelling with this catalyst takes place smoothly at ambient temperature in a mixture of N,N‐dimethylformamide and deuterium oxide.

Recyclable Catalysts for Alkyne Functionalization

In this review, we present an assessment of recent advances in alkyne functionalization reactions, classified according to different classes of recyclable catalysts. In this work, we have incorporated and reviewed the activity and selectivity of recyclable catalytic systems such as polysiloxane-encapsulated novel metal nanoparticle-based catalysts, silica-copper-supported nanocatalysts, graphitic carbon-supported nanocatalysts, metal organic framework (MOF) catalysts, porous organic framework (POP) catalysts, bio-material-supported catalysts, and metal/solvent free recyclable catalysts. In addition, several alkyne functionalization reactions have been elucidated to demonstrate the success and efficiency of recyclable catalysts. In addition, this review also provides the fundamental knowledge required for utilization of green catalysts, which can combine the advantageous features of both homogeneous (catalyst modulation) and heterogeneous (catalyst recycling) catalysis.

Hydroquinone and benzoquinone-catalyzed aqueous Knoevenagel condensation

A Knoevenagel condensation of various aldehydes with malononitrile effectively proceeded in the presence of hydroquinone/benzoquinone mixed catalysts at room temperature in H₂O. Furthermore, γ-deuterium-labeled α,β-unsaturated nitrile derivatives were also constructed via a deuteration of an aliphatic aldehyde in D₂O using a basic resin and the subsequent Knoevenagel condensation.

Divergent Elementoboration: 1,3-Haloboration versus 1,1-Carboboration of Propargyl Esters

This work showcases the 1,3-haloboration reaction of alkynes in which boron and chlorine add to propargyl systems in a proposed sequential oxazoliumborate formation with subsequent ring-opening and chloride migration. In addition, the functionalization of these propargyl esters with dimethyl groups in the propargylic position leads to stark differences in reactivity whereby a formal 1,1-carboboration prevails to give the 2,2-dichloro-3,4-dihydrodioxaborinine products as an intramolecular chelate. Density functional theory calculations are used to rationalize the distinct carboboration and haloboration pathways. Significantly, this method represents a metal-free route to highly functionalized compounds in a single step to give structurally complex products.

Catalytic selective deuteration of halo(hetero)arenes

Deuterium labeled aromatic and heteroaromatic compounds are synthesized in good to excellent yields with >98% deuterium purity via palladium catalyzed deuterodehalogenation reaction using commercially available and inexpensive reagents. Selective deuteration of bromoaniline is also demonstrated without H/D exchange in an amino N-H group.

The ruthenium-catalysed selective synthesis of mono-deuterated terminal alkynes

A highly efficient catalytic system is reported for chemoselective synthesis of mono-deuterated terminal alkynes using deuterium oxide in which the reaction proceeds via Ru–acetylide intermediates formed by selective activation of the sp-CH bond.