Unlocking Heteroaromatic Ring Systems through Chalcogen Insertion into Boroles

In this work, we report the reactivity of various annulated borole derivatives toward chalcogen (O, S, and Se) insertion. Among a series of 9-borafluorenes with different boron substituents (Ph, Br, or o-carboranyl) and a mixed thiophene-benzene-fused derivative, only the 9-o-carboranyl-substituted 9-borafluorene yielded the complete set of chalcogen-containing heteroarenes, including the first 1,2-selenaborinine derivative. To evaluate the aromaticity of this heterocyclic analogue of phenanthrene, nucleus-independent chemical shift (NICS) values were computed and compared to those of its lighter group 16 congeners.

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.

A Simple Zinc-Mediated Method for Selenium Addition to Michael Acceptors

In this work, we focused our attention on seleno-Michael type reactions. These were performed using zinc-selenolates generated in situ from diphenyl diselenide 1, 1,2-bis(3-phenylpropyl)diselenide 30, and protected selenocystine 31 via an efficient biphasic Zn/HCl-based reducing system. Alkenes with a variety of electron-withdrawing groups were investigated in order to gauge the scope and limitations of the process. Results demonstrated that the addition to acyclic α,β-unsaturated ketones, aldehydes, esters amides, and acids was effectively achieved and that alkyl substituents at the reactive β-centre can be accommodated. Similarly, cyclic enones undergo efficient Se-addition and the corresponding adducts were isolated in moderate to good yield. Vinyl sulfones, α,β-unsaturated nitriles, and chalcones are not compatible with these reaction conditions. A recycling experiment demonstrated that the unreacted Zn/HCl reducing system can be effectively reused for seven reaction cycles (91% conversion yield at the 7° recycling rounds).

Transition-metal-free B-B and B-interelement reactions with organic molecules

This review is a guided tour along the activation modes and reactivity of B-B, B-Si, B-N, B-S, B-Se and B-P reagents, in the absence of any transition metal complex. Here are disclosed the general concepts related to the homolytic and heterolytic cleavage of B-B and B-interelement bonds, as well as the generation of new C-B and C-interelement bonds, in a selective way. The greener consequences of these novel routes facilitate the gram scale preparations of target functionalised organic compounds. Intrinsic data about the suggested mechanisms and spectroscopic evidence that supports the innovative theories are provided along the review. Since this is a stimulating area of work that has emerged within the last decade, this overview serves as the basis to understand the new trends and hopefully to generate inspiration for future discoveries in the field.

Understanding the mechanism of transition metal-free anti addition to alkynes: the selenoboration case

A novel mechanism was proposed for the stereoselective anti-addition of selenoboranes to alkynes using catalytic amounts of PCy₃.

Ring-opening selenation of cyclobutanols: synthesis of γ-selenylated alkyl ketones through C–C bond cleavage

An efficient, practical, and operationally simple manganese-mediated ring-opening selenation of cyclobutanols is disclosed.

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.

sp(2)-sp(3) diboranes: astounding structural variability and mild sources of nucleophilic boron for organic synthesis

Despite the widespread use of organoborane reagents in organic synthesis and catalysis, a major challenge still remains: very few boron-centered nucleophiles exist for the direct construction of B-C bonds. Perhaps the most promising emerging solution to this problem is the use of sp(2)-sp(3) diboranes, in which one boron atom of a conventional diborane(4) is quaternised by either a neutral or anionic nucleophile. These compounds, either isolated or generated in situ, serve as relatively mild and convenient sources of the boryl anion [BR2](-) for use in organic synthesis and have already proven their efficacy in metal-free as well as metal-catalysed borylation reactions. This Feature article documents the history of sp(2)-sp(3) diborane synthesis, their properties and surprising structural variability, and their burgeoning utility in organic synthesis.

Organocatalytic functionalisation through boron chemistry

Diboron reagents can be activated both, from a metal or free-metal context, and consequently the addition of boryl units to unsaturated substrates proceeds sometimes with complementary selectivity. We highlight here the power of boron chemistry to functionalize molecules and provide new routes towards challenging compounds.

The phosphinoboration reaction

The synthesis of phosphinoboronate esters containing a single P-B bond is reported, together with preliminary reactivity studies towards a range of organic substrates. These compounds add readily to aldehydes, ketones, aldimines, and α,β-unsaturated enones to give primarily the corresponding 1,2-addition products containing a new P-C bond. The first examples of transition-metal-catalyzed phosphinoborations of C-C multiple bonds in which P-C and B-C bonds are formed in a single step are also disclosed; allenes react by a highly regioselective 1,2-addition whereas terminal alkynes undergo a formal 1,1-addition.