Copper Catalysis for Synthesizing Main-Group Organometallics Containing B, Sn or Si

Synthesis of Cyclic Allylborates from 1,3-Dienes and a Diboron Reagent

The synthesis of cyclic allylborates was achieved by the reaction of 1,3-dienes and B₂ pin₂ using a copper catalyst. Several 1,3-dienes were converted to the corresponding cyclic allylborates in moderate to high yields. The cyclic allylborate obtained could be used in several organic transformations such as allylation of electrophiles and Suzuki-Miyaura coupling.

First-Row d-Block Element-Catalyzed Carbon-Boron Bond Formation and Related Processes

Organoboron reagents represent a unique class of compounds because of their utility in modern synthetic organic chemistry, often affording unprecedented reactivity. The transformation of the carbon-boron bond into a carbon-X (X = C, N, and O) bond in a stereocontrolled fashion has become invaluable in medicinal chemistry, agrochemistry, and natural products chemistry as well as materials science. Over the past decade, first-row d-block transition metals have become increasingly widely used as catalysts for the formation of a carbon-boron bond, a transformation traditionally catalyzed by expensive precious metals. This recent focus on alternative transition metals has enabled growth in fundamental methods in organoboron chemistry. This review surveys the current state-of-the-art in the use of first-row d-block element-based catalysts for the formation of carbon-boron bonds.

Saturated Boronic Acids, Boronates, and Trifluoroborates: An Update on Their Synthetic and Medicinal Chemistry

This review discusses recent advances in the chemistry of saturated boronic acids, boronates, and trifluoroborates. Applications of the title compounds in the design of boron-containing drugs are surveyed, with special emphasis on α-amino boronic derivatives. A general overview of saturated boronic compounds as modern tools to construct C(sp³ )-C and C(sp³ )-heteroatom bonds is given, including recent developments in the Suzuki-Miyaura and Chan-Lam cross-couplings, single-electron-transfer processes including metallo- and organocatalytic photoredox reactions, and transformations of boron "ate" complexes. Finally, an attempt to summarize the current state of the art in the synthesis of saturated boronic acids, boronates, and trifluoroborates is made, with a brief mention of the "classical" methods (transmetallation of organolithium/magnesium reagents with boron species, anti-Markovnikov hydroboration of alkenes, and the modification of alkenyl boron compounds) and a special focus on recent methodologies (boronation of alkyl (pseudo)halides, derivatives of carboxylic acids, alcohols, and primary amines, boronative C-H activation, novel approaches to alkene hydroboration, and 1,2-metallate-type rearrangements).

Borylation and Stannylation Reactions with Tuning of Lewis Acidity

A B(dan) moiety (dan=naphthalene-1,8-diaminato) of diminished boron-Lewis acidity has efficiently been installed into organic frameworks by three-component carboboration of alkenes under copper catalysis, where a Cu-B(dan) species, generated by chemoselective σ-bond metathesis between a copper catalyst and an unsymmetrical diboron [(pin)B-B(dan)], acts as a key intermediate. The Cu-B(dan) species has also turned out to serve as a B(dan) nucleophile to afford various dan-substituted organoboranes via borylative substitution of carbon electrophiles. Furthermore, borylation reactions with another Lewis acidity-diminished boron unit, B(aam) (aam=anthranilamidato), have become feasible by use of (pin)B-B(aam) or H-B(aam). The resulting dan/aam-substituted organoboranes have been demonstrated to undergo direct cross-coupling without prior acidic deprotection, regardless of their diminished boron-Lewis acidity. Synthesis of diverse organostannanes based upon copper-catalyzed carbostannylation and borylstannylation, in which Lewis acidity increment of a tin center facilitates the progress in some cases, have also been described.

Copper-Catalyzed Chemoselective Silylative Cyclization of 2,2'-Diethynylbiaryl Derivatives

In this protocol, copper-catalyzed diverse silylative carbocyclization reactions of 2,2'-diethynylbiaryl derivatives with silaboronate were reported. Three new and novel types of domino reactions for the copper-catalyzed transformation of silaboronate were discovered. The corresponding cyclobuta[l]phenanthrene, bis((silyl)methyl)phenanthrene, and silyl-substituted exocyclic diene products were chemoselectively formed with high efficiency.

Ligand-Dependent-Controlled Copper-Catalyzed Regio- and Stereoselective Silaboration of Alkynes

A copper-catalyzed highly regio- and stereoselective silaboration of alkynes was developed. In this work, direct cis-difunctionalization of alkynes was realized with silaboronate reagent and copper catalyst in aprotic solvents. The regiodivergent silaborations were controlled by tuning the copper catalysts and phosphine ligands used in reactions. This protocol provides an efficient and practical method to synthesize the multisubstituted functionalized alkenes with specific stereoselectivity.

Copper-Catalyzed Trifunctionalization of Alkynes: Rapid Formation of Oxindoles Bearing Geminal Diboronates

A copper-catalyzed trifunctionalization of alkynes that provides rapid access to oxindoles bearing a geminal diboronate side chain, highlighted by the simultaneous formation of one C-C bond and two C-B bonds, is reported. This new reaction features simple reaction conditions (ligand-free catalysis), a general substrate scope, and excellent chemoselectivity. Mechanistic study revealed a reaction sequence constituted by, in the order, borylation, intramolecular cross-coupling, hydroboration, which has been rarely documented.

Selective uni- and bidirectional homologation of diborylmethane

Diborylmethane can be homologated uni- and bidirectionally by using enantiomerically pure lithium-stabilized carbenoids to give 1,2- and 1,3-bis(boronic esters), respectively, in good yield and with excellent levels of enantio- and diastereoselectivity. The high sensitivity of the transformation to steric hindrance enables the exclusive operation of either manifold, effected through the judicious choice of the type of carbenoid, which can be a sparteine-ligated or a diamine-free lithiated benzoate/carbamate. The scope of the 1,2-bis(boronic esters) so generated is complementary to that encompassed by the asymmetric diboration of alkenes, in that primary-secondary and primary-tertiary 1,2-bis(boronic esters) can be prepared with equally high levels of selectivity and that functional groups, such as terminal alkynes and alkenes, are tolerated. Methods for forming C2-symmetric and non-symmetrical anti and syn 1,3-bis(boronic esters) are also described and represent a powerful route towards 1,3-functionalized synthetic intermediates.

Copper-catalyzed direct borylation of alkyl, alkenyl and aryl halides with B(dan)

Copper-catalyzed reaction of organic halides with an unsymmetrical diboron, (pin)B–B(dan), which leads to the direct formation of masked organoboron compounds, is reported.

The phosphinoboration of carbodiimides, isocyanates, isothiocyanates and CO2

The transition metal-free addition of phosphinoboronate ester Ph₂PBpin (pin = 1,2-O₂C₂Me₄) to heterocumulenes including carbodiimides, isocyanates, isothiocyanates and carbon dioxide proceeds with remarkable selectivity to give products in high yield.

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

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.