The Cu(I)-catalyzed stereoconvergent borylative cyclization of ω-mesylate-α,β-unsaturated compounds is facilitated by a simple Cu-bisphosphine catalyst. This reaction provides a novel route to cis-β-boron-substituted five- and six-membered carbocycle and heterocycle esters. Mechanistic studies indicate that stereoconvergence and cis-substitution likely stem from the rapid enolation of the borylcopper adduct with the substrate double bond and the formation of a five-membered intermediate, respectively.

Boron-substituted 1,4-dienes are versatile building blocks for the synthesis of 1,4-dienes (skipped alkenes), a common motif in bioactive natural products, because of their utility in the Suzuki–Miyaura coupling reaction and conjugate additions. A method for the synthesis of boron-substituted 1,4-dienes by means of copper-catalyzed boryl–allylation of alkynes with allyl phosphate and bis(pinacolato)diboron has been developed. The regioselectivity with respect to the alkyne and allyl phosphate depends on the structures of both the alkyne and the allyl phosphate. For alkynes bearing at least one aryl substituent, addition of borylcopper to the alkyne mainly generates a β-boryl-α-aryl-α-alkenylcopper species, whose subsequent reaction with secondary allyl phosphates provides γ-(4E)-selective boron-substituted 1,4-dienes, and with primary allyl phosphates provided α-selective boron-substituted 1,4-dienes. On the other hand, the α-boryl-α-aryl-β-alkenylcopper species formed as a minor intermediate from aryl alkyl acetylenes and the β-borylalkenylcopper species formed from dialkyl acetylenes show poor regioselectivity with respect to the secondary allyl phosphate and produce a mixture of α- and γ-selective boron-substituted 1,4-dienes. However, their reactions with the primary allyl phosphate are highly γ-selective. For all of the α-selective reactions, the configuration of the C═C bond of the allyl phosphate was retained in the products. The palladium-catalyzed cross-coupling of boron-substituted 1,4-dienes and aromatic, alkenyl, and alkynyl halides gave polyenes or enynes in 68%–95% yield, demonstrating that these boron-substituted 1,4-dienes are versatile building blocks for the synthesis of 1,4-dienes.Keywords: 1,4-dienylboronate; alkyne; allyl phosphate; carboboration; copper catalysis

The Grubbs–Hoveyda type ruthenium–carbene complexes have been covalently immobilized on both silica coated and uncoated magnetic nanoparticles utilizing an imidazolium salt linker. These MNP-supported catalysts showed comparable catalytic activity to the homogeneous imidazolium salt-tagged ruthenium catalyst in the ring-closing metathesis (RCM) of dienes, and could effectively catalyze RCM reactions in the presence of only 0.85 mol % Ru. The MNP-supported ruthenium catalysts could be easily recovered using an external magnet. The recyclability of the silica-coated MNP-supported catalysts was superior to silica uncoated MNP-supported catalysts allowing reuse 14 times, due to the increased compatibility of the silica-coated MNPs with the reaction medium.

The Grubbs–Hoveyda ruthenium–carbene complex has been covalently immobilized on ionic magnetic nanoparticles utilizing an imidazolium salt linker. The supported catalyst exhibited excellent catalytic activity for ring-closing metathesis (RCM) and cross-metathesis (CM) in the presence of less than 1 mol % of ruthenium. The catalysts can easily be recovered magnetically and reused up to seven times with minimal leaching of ruthenium species.

The Cu(I)-catalyzed stereoconvergent borylative cyclization of ω-mesylate-α,β-unsaturated compounds is facilitated by a simple Cu-bisphosphine catalyst. This reaction provides a novel route to cis-β-boron-substituted five- and six-membered carbocycle and heterocycle esters. Mechanistic studies indicate that stereoconvergence and cis-substitution likely stem from the rapid enolation of the borylcopper adduct with the substrate double bond and the formation of a five-membered intermediate, respectively.