Although known for over 90 years, only in the past two decades has the chemistry of diboron(4) compounds been extensively explored. Many interesting structural features and reaction patterns have emerged, and more importantly, these compounds now feature prominently in both metal-catalyzed and metal-free methodologies for the formation of B–C bonds and other processes.

Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse

This Perspective illustrates the defining characteristics of free radical chemistry, beginning with its rich and storied history. Studies from our laboratory are discussed along with recent developments emanating from others in this burgeoning area. The practicality and chemoselectivity of radical reactions enable rapid access to molecules of relevance to drug discovery, agrochemistry, material science, and other disciplines. Thus, these reactive intermediates possess inherent translational potential, as they can be widely used to expedite scientific endeavors for the betterment of humankind.

Radicals: Reactive Intermediates with Translational Potential

Alkyl carboxylic acids are ubiquitous in all facets of chemical science, from natural products to polymers, and represent an ideal starting material with which to forge new connections. This study demonstrates how the same activating principles used for decades to make simple C–N (amide) bonds from carboxylic acids with loss of water can be used to make C–C bonds through coupling with dialkylzinc reagents and loss of carbon dioxide. This disconnection strategy benefits from the use of a simple, inexpensive nickel catalyst and exhibits a remarkably broad scope across a range of substrates (>70 examples).

http://science.sciencemag.org/content/sci/early/2016/04/20/science.aaf6123.full.pdf

A general alkyl-alkyl cross-coupling enabled by redox-active esters and alkylzinc reagents.

Recent Developments in Organoboron Chemistry: Old Dogs, New Tricks

Cross-Coupling and Related Reactions: Connecting Past Success to the Development of New Reactions for the Future

Transition metal catalysis plays a central role in contemporary organic synthesis. Considering the tremendously broad array of transition metal-catalyzed transformations, it is remarkable that the underlying elementary reaction steps are relatively few in number. Here, we describe an alternative to the organometallic transmetallation step that is common in many metal-catalyzed reactions, such as Suzuki-Miyaura coupling. Specifically, we demonstrate that vinyl boronic ester ate complexes, prepared by combining organoboronates and organolithium reagents, engage in palladium-induced metallate rearrangement wherein 1,2-migration of an alkyl or aryl group from boron to the vinyl α-carbon occurs concomitantly with C-Pd σ-bond formation. This elementary reaction enables a powerful cross-coupling reaction in which a chiral Pd catalyst merges three simple starting materials-an organolithium, an organoboronic ester, and an organotriflate-into chiral organoboronic esters with high enantioselectivity.

/pdf/catalytic-conjunctive-cross-coupling-enabled-by-metal-32gm78cded.pdf

Catalytic conjunctive cross-coupling enabled by metal-induced metallate rearrangement

Synthesis of Vinyl Boronates from Aldehydes by a Practical Boron–Wittig Reaction

The catalytic enantioselective diboration of vinyl boronate esters furnishes chiral tris(boronates) in a selective fashion. Subsequent deborylative alkylation occurs in a diastereoselective fashion, both for intermolecular and intramolecular processes.

http://pubs.acs.org/doi/pdf/10.1021/ja510081r

Enantiomerically enriched tris(boronates): readily accessible conjunctive reagents for asymmetric synthesis.

An alkoxide-catalyzed directed diboration of alkenyl alcohols is described. This reaction occurs in a stereoselective fashion and is demonstrated with cyclic and acyclic homoallylic and bishomoallylic alcohol substrates. After oxidation, the reaction generates 1,2-diols such that the process represents a method for the stereoselective directed dihydroxylation of alkenes.

http://pubs.acs.org/doi/pdf/10.1021/ja504228p

Hydroxyl-directed stereoselective diboration of alkenes.

Enantio- and diastereoselective conjunctive cross-coupling of β-substituted alkenylboron “ate” complexes is studied. Whereas β-substitution shifts the chemoselectivity of the catalytic reaction in favor of the Suzuki–Miyaura product, use of a boronic ester ligand derived from acenaphthoquinone allows the process to favor the conjunctive product, even with substituted substrates.

/pdf/diastereoselective-and-enantioselective-conjunctive-cross-5bgubfm8t1.pdf

Liang Zhang

Papers

Catalytic conjunctive cross-coupling enabled by metal-induced metallate rearrangement

Synthesis of Vinyl Boronates from Aldehydes by a Practical Boron–Wittig Reaction

Enantiomerically enriched tris(boronates): readily accessible conjunctive reagents for asymmetric synthesis.

Hydroxyl-directed stereoselective diboration of alkenes.

Diastereoselective and Enantioselective Conjunctive Cross-Coupling Enabled by Boron Ligand Design.