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Updated: May 13, 2026
11:45
Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
Published on: August 22, 2018
Cycloaddition reactions between dicyclohexylboron azide and alkynes.
Rebecca L Melen1, Douglas W Stephan
1Department of Chemistry, 80 St. George Street. and University of Toronto, Toronto, Ontario, Canada M5S 3H6.
Dalton Transactions (Cambridge, England : 2003)
|February 26, 2013
Summary
New boron azide reactions yield novel 1,2,3-triazoles. Room temperature cycloadditions with electron-poor alkynes create unique cyclic compounds, including a macrocycle.
Area of Science:
- Organic Chemistry
- Synthetic Chemistry
- Heterocyclic Chemistry
Background:
- 1,3-Dipolar cycloaddition reactions are fundamental in organic synthesis.
- Boron azides are reactive dipoles with unique chemical properties.
- Electron-poor alkynes are versatile building blocks for heterocyclic synthesis.
Purpose of the Study:
- To investigate the reactivity of boron azide (Cy2BN3) in 1,3-dipolar cycloaddition reactions.
- To synthesize novel 1,2,3-triazole derivatives using boron azide and various electron-poor alkynes.
- To explore the formation of macrocyclic products in these cycloaddition reactions.
Main Methods:
- Room temperature 1,3-dipolar cycloaddition reactions.
- Utilized boron azide (Cy2BN3) as the 1,3-dipole.
- Employed electron-poor acetylenes: RCO2C≡CCO2R, EtC≡CCOMe, and HC≡CP(=O)Ph2.
- Characterization of synthesized triazole products.
Main Results:
- Successfully synthesized new 1,2,3-triazoles via cycloaddition of Cy2BN3 with electron-poor alkynes.
- Observed the formation of a novel macrocyclic product when reacting with RCO2C≡CCO2R.
- The macrocycle formation involved the loss of the R group.
Conclusions:
- Boron azide is an effective reagent for the synthesis of 1,2,3-triazoles.
- The reaction conditions allow for the formation of complex macrocyclic structures.
- This study expands the scope of 1,3-dipolar cycloaddition chemistry involving organoboron compounds.
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02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
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.
02:38Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
02:27Preparation of Alkynes: Alkylation Reaction
Introduction
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
02:35Electrophilic Addition to Alkynes: Hydrohalogenation
Electrophilic addition of hydrogen halides, HX (X = Cl, Br or I) to alkenes forms alkyl halides as per Markovnikov's rule, where the hydrogen gets added to the less substituted carbon of the double bond. Hydrohalogenation of alkynes takes place in a similar manner, with the first addition of HX forming a vinyl halide and the second giving a geminal dihalide.
02:34Preparation of Alkynes: Dehydrohalogenation
Introduction
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.
03:08Hydroboration-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.