Ortho-Cyclization in Asymmetrically Substituted Arylnitroso Oxides
Ekaterina M Chainikova1, Sergey L Khursan1, Alfia R Yusupova1
1Ufa Institute of Chemistry, Ufa Federal Research Center of the Russian Academy of Sciences, 71 pr. Oktyabrya, Ufa 450054, Russian Federation.
The Journal of Organic Chemistry
|July 22, 2020
Summary
Photooxidation of phenyl azides forms nitroso oxides, which cyclize to nitrile oxides. These then react with acetonitrile, yielding 1,2,4-oxadiazoles, with regioselectivity influenced by substituents.
Area of Science:
- Organic Chemistry
- Photochemistry
- Reaction Mechanisms
Background:
- Phenyl azides undergo photooxidation in acetonitrile.
- Nitroso oxides are key intermediates in this process.
- The reaction pathway involves unimolecular consumption of nitroso oxides.
Purpose of the Study:
- To elucidate the mechanism of photooxidation of asymmetrically substituted phenyl azides.
- To investigate the factors influencing the regioselectivity of nitroso oxide cyclization.
- To understand the role of substituents in directing the reaction pathway.
Main Methods:
- Photochemical reaction studies in acetonitrile.
- Spectroscopic analysis of intermediates and products.
- Theoretical calculations to explain regioselectivity.
Main Results:
- Photooxidation yields nitroso oxides which cyclize to nitrile oxides.
- Regioselectivity of cyclization is influenced by substituents, particularly para-methoxy groups.
- Nitrile oxides undergo [3+2] cycloaddition with acetonitrile to form 1,2,4-oxadiazoles.
Conclusions:
- The mechanism involves ortho-cyclization of nitroso oxides to form nitrile oxides.
- Stereoelectronic effects of para-methoxy substituents dictate regioselectivity.
- The study provides insights into the photochemical behavior of substituted phenyl azides.
![Solid-phase Synthesis of [4.4] Spirocyclic Oximes](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F58508.jpg&w=3840&q=50)
Related Concept Videos
01:11ortho–para-Directing Activators: –CH3, –OH, –NH2, –OCH3
7.1K
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
7.1K
01:30Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)
4.5K
Nucleophilic substitution in aromatic compounds is feasible in substrates bearing strong electron-withdrawing substituents positioned ortho or para to the leaving group. The reaction proceeds via two steps: the addition of the nucleophile and the elimination of the leaving group.
The reaction begins with an attack of the nucleophile on the carbon that holds the leaving group. This results in the delocalization of the π electrons over the ring carbons. The resonance interaction between...
The reaction begins with an attack of the nucleophile on the carbon that holds the leaving group. This results in the delocalization of the π electrons over the ring carbons. The resonance interaction between...
4.5K
01:19Nitrosation of Enols
7.7K
The nitrosation reaction is one of the methods of preparing 1,2-diketones. The enol tautomer of the starting ketone reacts with sodium nitrite in hydrochloric acid, generating the 1,2-diketone after hydrolysis.
7.7K
01:17Reactions of α-Halocarbonyl Compounds: Nucleophilic Substitution
3.8K
Nucleophilic substitution in α-halocarbonyl compounds can be achieved via an SN2 pathway. The reaction in α-haloketones is generally carried out with less basic nucleophiles. The use of strong basic nucleophiles leads to the generation of α-haloenolate ions, which often participate in other side reactions.
3.8K
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
20.3K
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.
20.3K
01:27Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation
2.7K
Robinson annulation is a base-catalyzed reaction for the synthesis of 2-cyclohexenone derivatives from 1,3-dicarbonyl donors (such as cyclic diketones, β-ketoesters, or β-diketones) and α,β-unsaturated carbonyl acceptors. Named after Sir Robert Robinson, who discovered it, this reaction yields a six-membered ring with three new C–C bonds (two σ bonds and one π bond).
2.7K