Iron-Catalyzed Diborylation of Unactivated Aliphatic gem-Dihalogenoalkenes: Synthesis of 1,2-Bis(boryl)alkanes

The current utility and future potential of multiborylated alkanes

Organoboron chemistry has become a cornerstone of modern synthetic methodology. Most of these reactions use an organoboron starting material that contains just one C(sp2)-B or C(sp3)-B bond; however, there has been a recent and accelerating trend to prepare multiborylated alkanes that possess two or more C(sp3)-B bonds. This is despite a lack of general reactivity, meaning many of these compounds currently offer limited downstream synthetic value. This Review summarizes recent advances in the exploration of multiborylated alkanes, including a discussion on how these products may be elaborated in further synthetic manipulations.

Alkoxide-Assisted Stereoselective Functionalization of 1,2-Bis-boronic Esters Under Photoredox Catalysis

Site-specific functionalization of the secondary C-B bond of 1,2-bis-boronic esters has been proven to be an important method for the generation of 1,2-bis-functionalized compounds in a highly stereoselective manner. We have explored previously unknown secondary selective alkenylation, allylation, alkynylation and addition to aryl vinyl trifluoromethane, which proceeds via a novel reaction mechanism: alkoxide-mediated photoredox activation to generate secondary radicals over the primary one.

Understanding the Mechanism and Selectivity of 1,1-Diborylalkanes from Alkenes Catalyzed by a Zirconium Complex

The synthesis of 1,1-diborylalkanes from readily available alkenes is an appealing method. The density functional theory (DFT) method was employed to investigate the reaction mechanism of 1,1-diborylalkanes, which was synthesized from alkenes and a borane, and the reaction was catalyzed by a zirconium complex Cp₂ZrCl₂. The entire reaction is divided into two cycles: dehydrogenative boration to form vinyl boronate esters (VBEs) and hydroboration of VBEs. This article focuses on the hydroboration cycle and elaborates on the role of the reducing reagents in the equilibrium of self-contradictory reactivity (dehydrogenative boration and hydroboration). The H₂ and HBpin pathways were investigated as the reducing reagents in the hydroboration process. The calculated results showed that it is more advantageous to use H₂ as a reducing agent (path A). Furthermore, the σ-bond metathesis is the rate-determining step (RDS) with an energetic span of 21.4 kcal/mol. This is consistent with the self-contradictory reactivity balance proposed in the experiment. The reaction modes of the hydroboration process were also discussed. These analyses revealed the origin of selectivity in this boration reaction, in which the σ-bond metathesis of HBpin needs to overcome the strong interaction between HBpin and the Zr metal. Meanwhile, the origin of the selectivity of different positions of H₂ is the interaction between the σ(H¹-H²) → σ*(Zr¹-C¹) overlap and these findings have implications for catalyst design and application.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Diverse reactivity of the gem-difluorovinyl iodonium salt for direct incorporation of the difluoroethylene group into N- and O-nucleophiles

The synthesis of gem-difluoroethylene compounds remains a difficult task in organic synthesis. Here, the direct difluoroethylation reactions of N- and O-nucleophiles including amides and acids were realized with a hypervalent iodine reagent: gem-difluorovinyl iodonium salt (DFVI). The reactions were accomplished via a neighbouring group rearrangement. The gem-difluorovinyl iodonium salt was found to display diverse reactivity due to its unique electronic effect and was applied to the incorporation of difluoroethylene group, including difluorovinylation of carboxylic acids, difluorovinylation and 1,3-cyclic fluorovinylation of amides and 1,1-cyclic difluoroethylation of amines.

Nickel(II)-catalyzed highly selective 1,2-diborylation of non-activated monosubstituted alkenes

A practical method for 1,2-diborylation of non-activated monosubstituted alkenes via nickel catalysis has been developed. The protocol features high functional group tolerance and can be applied for the formal synthesis of drugs and modification of natural product derivatives. Preliminary mechanistic studies imply the involvement of a Ni(II) catalytic cycle.

Boron-Promoted Umpolung Reaction of Sulfonyl Chlorides for the Stereospecific Synthesis of Thioglycosides via Reductive Deoxygenation Coupling Reactions

S-Glycosides have broad biological activities and serve as stable mimics of natural O-glycoside counterparts and thus are of great therapeutic potential. Herein we disclose an efficient method for the stereospecific synthesis of 1-thioglycosides via a boron-promoted reductive deoxygenation coupling reaction from readily accessible sulfonyl chlorides and glycosyl bromides. Our protocol features mild conditions and excellent functional group tolerance and stereoselectivity. The translational potential of this metal-free approach is demonstrated by the late-stage glycodiversification of natural products and drug molecules.

Csp3‒H Monofluoroalkenylation via Stereoselective C‒F Bond Cleavage

A practical nickel- and photoredox-catalyzed Csp3‒H monofluoroalkenylation through chelation-assisted Csp2‒F bond cleavage of gem-difluoroalkenes has been developed, which provides an expedient access to the synthesis of tetrasubstituted fluoroalkenes with complete...

Advances in silylation and borylation of fluoroarenes and gem-difluoroalkenes via C-F bond cleavage

Organoboron and organosilane compounds are widely used in organic synthesis and pharmaceuticals. In addition, the C-F bond functionalization is a useful tool for the construction of carbon-carbon and carbon-heteroatom bonds. In particular, the late-stage functionalization of bioactive molecules through defluoroborylation and defluorosilylation reactions will provide good opportunities for the development and diversification of new medicinal compounds. Thus, this feature article summarized the methods for the defluorosilylation and defluoroborylation of unreactive monofluoroarenes and gem-difluoroalkenes from 2000 to 2021, which might create some new ideas and will be helpful for further research in this field. These defluoroborylation and defluorosilylation strategies can be applied to synthesize silylated arenes, borylated arenes, silylated fluoroalkenes, and borylated fluoroalkenes, thus providing impressive advantages over traditional methods for the synthesis of organoboron and organosilane compounds in terms of divergent structures.

Iron-catalyzed C–F bond silylation and borylation of fluoroarenes

Iron-catalyzed functionalization of inert bonds has scarcely been documented.