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Regioselectivity and Stereochemistry of Hydroboration

Regioselectivity and Stereochemistry of Hydroboration

A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.

Hydroboration-Oxidation of Alkenes

Hydroboration-Oxidation of Alkenes

In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.

Radical Substitution: Allylic Bromination

Radical Substitution: Allylic Bromination

In organic synthesis, the formation of products can be altered by changing the reaction conditions. For example, a dibromo addition product is formed when propene is treated with bromine at room temperature. In contrast, propene undergoes allylic substitution in non-polar solvents at high temperatures to give 3-bromopropene. In order to avoid the addition reaction, the bromine concentration must be kept as low as possible throughout the reaction. This can be achieved using N-bromosuccinimide...

Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene

Electrophilic 1,2- and 1,4-Addition of X₂ to 1,3-Butadiene

Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium ion to form a 1,2-dihalide or a vicinal dihalide.

Halogenation of Alkenes

Halogenation of Alkenes

Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.

Cycloaddition Reactions: MO Requirements for Thermal Activation

Cycloaddition Reactions: MO Requirements for Thermal Activation

Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.

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Updated: Feb 20, 2026

Synthesis of a Borylated Ibuprofen Derivative Through Suzuki Cross-Coupling and Alkene Boracarboxylation Reactions

Synthesis of a Borylated Ibuprofen Derivative Through Suzuki Cross-Coupling and Alkene Boracarboxylation Reactions

Published on: November 30, 2022

Coordination and Insertion: Competitive Channels for Borylene Reactions.

Kelling J Donald¹, Ezana Befekadu¹, Supreeth Prasad¹

¹Department of Chemistry, Gottwald Center for the Sciences, University of Richmond , Richmond, Virginia 23173, United States.

The Journal of Physical Chemistry. A

|October 27, 2017

Summary

Monovalent boron (borylene) species are unstable but can form complexes with carbon, silicon, and germanium. Their reactivity and stability depend on the boron substituent and the metal, influencing their synthetic potential.

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Area of Science:

Inorganic Chemistry
Organic Synthesis
Computational Chemistry

Background:

Monovalent boron (borylene) species (B-R) are highly unstable, limiting their study and application in synthesis.
Existing literature has significant gaps regarding the utility of borylenes as ligands or reaction intermediates.

Purpose of the Study:

To investigate the stability and reactivity of borylene complexes with varying R groups.
To explore the interactions between borylenes and saturated carbon, silicon, and germanium centers.
To elucidate the factors governing borylene insertion reactions and complex formation.

Main Methods:

Computational chemistry methods, including MP2(full), CCSD(T), and B3LYP-D3 levels of theory.
Analysis of sigma hole interactions, dative bonding, and insertion reaction pathways.
Investigation of singlet-triplet state preferences in borylenes.

Main Results:

Borylene complex stability is strongly influenced by the electron-donating ability of the R group.
Borylenes form weak sigma hole interactions with carbon and stronger dative bonds with silicon and germanium.
Insertion reactions into M-H bonds compete with dative bonding, being barrierless for silicon and some germanium cases.
Monovalent boron complexes are stabilized by high insertion barriers when bonded to carbon.
Reactivity is sensitive to the nucleophilicity of the borylene species.

Conclusions:

Borylenes exhibit tunable stability and reactivity based on their substituents and bonding partners.
Computational insights reveal pathways for borylene complexation and insertion, highlighting potential synthetic applications.
The singlet state is preferred for borylenes, facilitating reactions with silicon.