Nickel-Catalyzed Migratory Benzylboration of Allylbenzenes

Stereoselective Construction of Multifunctional C-Glycosides Enabled by Nickel-Catalyzed Tandem Borylation/Glycosylation

Stereochemically pure saccharides have indispensable roles in fields ranging from medicinal chemistry to materials science and organic synthesis. However, the development of a simple, stereoselective, and efficient glycosylation protocol to access α- and β-C-glycosides (particularly 2-deoxy entities) remains a persistent challenge. Existing studies have primarily focused on C1 modification of carbohydrates and transformation of glycosyl radical precursors. Here, we innovate by harnessing the in situ generated glycosyl-Ni species to achieve one-pot borylation and glycosylation in a cascade manner, which is enabled by an earth-abundant nickel-catalyzed carboboration of readily accessible glycals without any ligand. This work reveals the potential for the development of a modular and multifunctional glycosylation platform to facilitate the simultaneous introduction of C-C and C-B bonds at the stereogenic center of saccharides, a largely unexploited research area. Preliminary experimental and computational studies indicate that the endocyclic O and the C3 group play important roles in stereoseclectively forging glycosidic bonds. As a result, a diverse range of C-R (R = alkyl, aryl, and alkenyl) and 2-deoxygenated glycosides bearing modifiable boron groups could be rapidly made with excellent stereocontrol and exhibit remarkable functional group tolerance. The synthetic potential is underscored in the late-stage glycosylation of natural products and commercial drugs as well as the facile preparation of various rare sugars, bioactive conjugates, and key intermediates to prorocentin, phomonol, and aspergillide A.

Regiodivergent sp3 C-H Functionalization via Ni-Catalyzed Chain-Walking Reactions

The catalytic translocation of a metal catalyst along a saturated hydrocarbon side chain constitutes a powerful strategy for enabling bond-forming reactions at remote, yet previously unfunctionalized, sp3 C-H sites. In recent years, Ni-catalyzed chain-walking reactions have offered counterintuitive strategies for forging sp3 architectures that would be difficult to accomplish otherwise. Although these strategies have evolved into mature tools for advanced organic synthesis, it was only recently that chemists showed the ability to control the motion at which the catalyst "walks" throughout the alkyl chain. Specialized ligand backbones, additives and a judicious choice of noninnocent functional groups on the side chain have allowed the design of "a la carte" protocols that enable regiodivergent bond-forming scenarios at different sp3 C-H sites with distinct topological surface areas. Given the inherent interest in increasing the fraction of sp3 hybridized carbons in medicinal chemistry, Ni-catalyzed regiodivergent chain-walking reactions might expedite the access to target leads in drug discovery campaigns.

Nickel Chain-Walking Catalysis: A Journey to Migratory Carboboration of Alkenes

ConspectusChain-walking offers extensive opportunities for innovating synthetic methods that involve constructing chemical bonds at unconventional sites. This approach provides previously inaccessible retrosynthetic disconnections in organic synthesis. Through chain-walking, transition metal-catalyzed alkene difunctionalization reactions can take place in a 1,n-addition (n ≠ 2) mode. Unlike classical 1,2-regioselective difunctionalization reactions, there remains a scarcity of reports regarding migratory patterns. Moreover, the range of olefins utilized in these studies is quite limited.About five years ago, our research group embarked on a project aimed at developing valuable migratory difunctionalization reactions of alkenes through chain-walking. Our focus was on carboboration of alkenes utilizing nickel catalysis. The reaction commences with the migratory insertion of an olefin into a Ni-Bpin species. Subsequently, a thermodynamically stable alkyl nickel complex is generated through a chain-walking process. This complex then couples with a carbon-based electrophile, leading to the formation of an alkylboron compound. It is worth highlighting that the success of these transformations relies significantly on the utilization of a bisnitrogen-based ligand and LiOMe as a B2pin2 activator. Synthetically, these migratory carboboration reactions establish a robust platform for the rapid and efficient synthesis of a wide range of structurally diverse organoboron compounds, which are not facially accessed by conventional methods. The incorporation of a versatile boron group introduces a wealth of possibilities for subsequent diversifications, significantly enhancing the value of the resulting products and allowing for the creation of a broader range of valuable derivatives and applications.This Account provides a comprehensive overview of our research efforts and advancements in the field of migratory carboboration of unactivated alkenes using nickel catalysis. We begin by outlining the development of a series of 1,1-regioselective carboboration reactions of terminal alkenes. A significant focus is placed on the initial integration of boronate, which not only triggers the formation of thermodynamically stable metal species but also exerts control over remote stereochemistry in reactions involving substituted methylenecyclohexenes. Continuing our exploration, remarkable success is achieved in 1,3-regio- and cis-stereoselectivity when dealing with cyclic alkenes. Remarkably, nickel chain-walking catalysis enables heterocyclic alkenes to be viable coupling partners within our transformations. Moreover, it grants us the ability to achieve regioselectivity for cyclohexenes that was previously unattainable, thus expanding the horizons of regiochemical control in these reactions. Lastly, we present the evolution of ligand-modulated regiodivergent carboboration of allylarenes. By gaining insights into the underlying mechanisms driving regiodivergence, we lay a strong foundation for tackling challenges related to selecting specific sites in chain-walking reactions, especially when dealing with multiple stable factors. We anticipate that our findings, coupled with the mechanistic insights we've gained, will not only advance the realm of nickel chain-walking catalysis but also contribute to the broader understanding of selectivity control in reactions of this nature. This advancement will also catalyze the synthesis of intricate functional molecules, contributing to the creation of complex and valuable compounds in the realm of organic chemistry.

Palladium-Catalyzed Hydroboration/Cyclization of 1,n-Dienes

While the hydroboration of alkenes is well established, the corresponding cyclization reaction of dienes remains challenging. Here, we report a new method for hydroboration/cyclization applicable to various 1,n-dienes and hydroboranes. The method features the direct synthesis of borylalkyl cyclopentanes from common 1,6-dienes, which is highlighted by syntheses of elaborated pyrrolidine cores from easily accessible diallylamines. Notably, 1,n-dienes (n > 6) also undergo five-membered ring formation, offering "remote" hydroboration/cyclization that would be otherwise difficult to achieve.