Abstract
Catalytic functionalization of alkynes with organoboron reagents provides a straightforward access to stereochemically defined multisubstituted alkenes, which are structural motifs commonly found in bioactive compounds and organic materials. Recent progress has substantially broadened the scope of this field on several fronts. Strategies for regioselectivity control in the 1,2-migratory insertion across unsymmetrical internal alkynes, as well as for the direct access to products with anti-insertion stereochemistry, have been devised. The alkenyl-to-aryl 1,4-metal migration upon metal insertion has been recently exploited in powerful cascade sequences leading to complex polycyclic scaffolds, including the development of enantioselective processes. Elegant enantiospecific and dynamic kinetic resolution methods have been developed for accessing chiral allenes from propargylic alcohol derivatives. Mechanistic manifolds have emerged based on single-electron transfer (SET) that have provided a fresh impetus for alkyne 1,2-difunctionalization with complementary stereoselectivity to processes relying on 1,2-insertion of R–M species. Herein, we discuss the most recent advances in transition-metal-catalyzed functionalization of alkynes using organoboron reagents, categorized according to the type of mechanistic outcome. Emphasis is placed on mechanistic aspects, synthetic utility, limitations, and challenges for future research.
Highlights
Transition-metal-catalyzed π-insertion processes across the triple bond of alkynes[1] allow straightforward access to stereochemically defined multifunctional olefins which are pivotal structural motifs found in bioactive compounds[2] and advanced materials[3] and versatile building blocks in synthetic chemistry[4] (Figure 1)
Organic boron reagents rank among the most prevalent class of coupling partners because of their stability, ready availability, and ease of handling.[5]. Merging these two fruitful chemistries has been the subject of intense research activities since the pioneering rhodium- and palladiumcatalyzed hydroarylation of alkynes with boronic acids reported by Hayashi[6] and Oh,[7] respectively, at the turn of the 21st century
Part II of this Review focuses on methods where the organoboron reagent participates in the last step of the functionalization of the triple bond, generally by trapping of the in situ generated alkenyl-metal intermediate (Scheme 1, 1.2)
Summary
Transition-metal-catalyzed π-insertion processes across the triple bond of alkynes[1] allow straightforward access to stereochemically defined multifunctional olefins which are pivotal structural motifs found in bioactive compounds[2] and advanced materials[3] and versatile building blocks in synthetic chemistry[4] (Figure 1). General Strategies for the Catalytic Functionalization of C−C Triple Bonds with Organoboron Reagents and the Scope of the Review application to the synthesis of heterocycles.[10] to the best of our knowledge, there is no previous review on transition-metal-catalyzed functionalization of alkynes with organoboron reagents, even though major advances in the past decade have substantially broadened the scope of this field on several fronts. This Review is divided into three parts, the first two of which deal with polar reaction mechanisms, whereas the third part focuses on radical reactions.
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