The copper-catalyzed sequential hydroboration of terminal alkynes with pinacolborane to prepare 1,1-diborylalkanes directly from alkynes was studied. Protected propargyl amines, propargyl alcohol derivatives, and simple alkynes regioselectively produced the desired 1,1-diborylalkanes in good yields with a copper/xantphos catalyst.

The development of catalytic Cu-B additions to carbon–carbon unsaturated bonds (borylcupration) with high regio- and stereoselectivity has enabled facile and direct syntheses of alkenylboronic esters, which are versatile synthetic intermediates in organic synthesis. An increasing number of relevant reactions have been reported over the past several years, which can be categorized based on the electrophilic reagent that reacts with the common alkenylcopper intermediates that are generated in situ by Cu-B addition to alkynes. In this Focus Review, recent advances in copper-catalyzed boron addition reactions for the synthesis of alkenylboronic esters with diboron reagents are summarized.

An efficient asymmetric addition of pinacolborane to 4-substituted coumarins proceeded with high enantioselectivity in the presence of a copper(I)-QuinoxP complex as a catalyst to produce the corresponding 1,4-hydroboration products. Treatment of the intermediates with electrophiles, without isolation, resulted in enantioenriched dihydrocoumarins. The utility of this protocol was demonstrated in the formal synthesis of biologically active molecules.

An efficient method for the preparation of enantiomerically enriched 1,1-diarylalkyl units has been developed. The use of copper hydride complexed by the (R)-1-[(S)-2-diphenylphosphino)ferrocenyl]ethyldicyclohexylphosphine (Josiphos) ligand effects a highly enantioselective conjugate reduction of β,β-diaryl-substituted α,β-unsaturated nitriles with aryl groups of similar steric demand and no secondary coordination site. A range of substrates with meta and para substituents on the aryl group were reduced with good to excellent enantioselectivities (up to 97 % enantiomeric excess (ee)) and this methodology was applied to the formal synthesis of indatraline.