Related Experiment Video
Updated: Jul 12, 2025
07:36
Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy
Published on: November 9, 2019
8.0K
Mechanistic Insight from Lewis-Acid-Dependent Selectivity and Reversible Haloboration, as Harnessed for Boron-Based
Martin Stang1, Robert J Mycka1,2, Suzanne A Blum1
1Department of Chemistry, University of California, Irvine, California 92697-2025, United States.
The Journal of Organic Chemistry
|October 25, 2023
Summary
Lewis acids like BBr3 exhibit reversible alkyne haloboration, enabling access to cyclic sulfonium zwitterions through controlled electrophilic cyclization. This offers predictable synthesis of valuable organic building blocks.
Area of Science:
- Organic Chemistry
- Organoboron Chemistry
- Synthetic Methodology
Background:
- Lewis acids, including boron compounds, are crucial catalysts in organic synthesis.
- Understanding reaction selectivity and the interplay of kinetics and thermodynamics is key to controlling synthetic outcomes.
- Boron trihalides and catecholboranes are versatile reagents with tunable reactivity.
Purpose of the Study:
- To investigate the reaction selectivity of different boron Lewis acids (ClBcat, BrBcat, BBr3) with alkynes.
- To explore the influence of tethered nucleophile chain length on reaction pathways.
- To elucidate the kinetic and thermodynamic control in reactions involving reversible haloboration.
Main Methods:
- Utilized B-chlorocatecholborane (ClBcat), B-bromocatecholborane (BrBcat), and Boron tribromide (BBr3) as Lewis acids.
- Employed NMR spectroscopy to monitor reaction reversibility.
- Characterized kinetic and thermodynamic products using 2D NMR and single-crystal X-ray diffraction.
Main Results:
- Observed distinct reaction selectivity: alkyne haloboration, electrophilic cyclization, or group transfer, dependent on the Lewis acid and nucleophile.
- Demonstrated that BBr3-mediated alkyne haloboration is reversible, allowing access to thermodynamically favored cyclic sulfonium zwitterions.
- Showcased BrBcat exhibiting intermediate reactivity between ClBcat and BBr3.
Conclusions:
- The reversibility of boron Lewis acid-mediated haloboration is a critical factor for accessing alternative reaction pathways.
- Predictable control over organic synthesis can be achieved by understanding and harnessing these reversible reactions.
- This work provides a foundation for utilizing boron Lewis acids to generate complex organic building blocks.
Related Concept Videos
02:36Regioselectivity and Stereochemistry of Hydroboration
8.2K
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...
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...
8.2K
03:08Hydroboration-Oxidation of Alkenes
8.3K
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.
8.3K
02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
14.3K
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
14.3K
02:46Halogenation of Alkenes
15.7K
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.
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.
15.7K
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
18.2K
Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
18.2K
02:15Preparation of Alcohols via Addition Reactions
6.3K
Overview
The acid-catalyzed addition of water to the double bond of alkenes is a large-scale industrial method used to synthesize low-molecular-weight alcohols. An acidic atmosphere is required to allow the hydrogen in the water molecule to act as an electrophile and attack the double bond in an alkene. The addition of a proton to the double bond creates a carbocation intermediate. The proton preferentially bonds to the less substituted end of the double bond to create a more stable carbocation...
The acid-catalyzed addition of water to the double bond of alkenes is a large-scale industrial method used to synthesize low-molecular-weight alcohols. An acidic atmosphere is required to allow the hydrogen in the water molecule to act as an electrophile and attack the double bond in an alkene. The addition of a proton to the double bond creates a carbocation intermediate. The proton preferentially bonds to the less substituted end of the double bond to create a more stable carbocation...
6.3K