Tri-and tetrasubstituted alkene scaffolds are prominent building blocks in many bioactive natural products, drug molecules, and key intermediates in various synthetic transformations. The dual functionalization of alkynes promises an easy introduction of functional groups across the triple bond with a high step and atom economy, exemplifying a class of reactions to construct tri-and tetrasubstituted alkene scaffolds. This review discusses the versatility and advances in the transition metal-catalyzed redox dual functionalization of alkynes, their unique mechanistic features, and the synthetic applications of the methodology. This collection focuses on the formation of simultaneous CÀ C/ CÀ X bonds involving various oxidation states of the metals in the catalytic cycle. Apart from the classical redox reactivity, radical-mediated functionalizations are also discussed in detail.
This paper presents the protoboration of 1,3-diynes as a platform for the iterative functionalization of various groups on enynes and dienes. Synthetic approaches to targets with high complexity are directed toward using small, modular building blocks similar to a “Lego” construction using iterative chemistry and automated synthesis. Organoboron compounds are currently in the spotlight for achieving these goals. Here, we report an operationally simple, regioselective protoboration of 1,3-diynes using a mixed diboron reagent and Cu(I)/phosphine catalyst to provide enynylboronates in good yields. Under similar conditions, diprotoboration of 1,3-diynes was also achieved to access bench-stable 1,4-diboryl-1,3-dienes in good yields and regioselectivities. The iterative coupling capabilities of the products have been demonstrated along with other downstream transformations offering a range of value-added skeletons.
In recent years, synergistic dual catalysis has been in the spotlight as a robust strategy for carbonÀ carbon and carbonÀ heteroatom bond formation. This review highlights the unique strategies of dual catalysis achieved in the past two decades, involving Pd-catalyst combined with various first-and second-row transition metals (like Cr, Fe, Cu, Ru, etc.), Lewis acids (based on Yb, Mg, Ti, Al, etc.) or organocatalysts (like squaramide, CPA, and NHC) to achieve valuable heterocyclic cores. Heterocycles find wide applications in pharmaceutical and agrochemical industries. Several organocatalysts like chiral phosphoric acid, NHC, squaramide, etc., and metal salts work in synergy with palladium to provide high-value products taking advantage of the vast development in cross-coupling reactions. This review is a comprehensive collection of such dual-catalysis strategies.
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