Photolysis of Chiral 1-Pyrazolines to Cyclopropanes:  Mechanism and Stereospecificity

Elena Muray; Ona Illa; José A. Castillo; Ángel Álvarez-Larena; José L. Bourdelande; Vicenç Branchadell; Rosa M. Ortuño

doi:10.1021/jo0342471

Photolysis of Chiral 1-Pyrazolines to Cyclopropanes: Mechanism and Stereospecificity

Elena Muray, Ona Illa, José A. Castillo, Ángel Álvarez-Larena, José L. Bourdelande, Vicenç Branchadell, Rosa M. Ortuño

Department of Chemistry

Research output: Contribution to journal › Article › Research › peer-review

18 Citations (Scopus)

Abstract

The photodenitrogenation of chiral trisubstituted 1-pyrazolines has been studied by laser flash photolysis. These experiments have permitted the detection of two transients that have been assigned, for each pyrazoline, to the trimethylene-type diradical resultant from the extrusion of nitrogen (lifetime τ = 0.1-0.8 μs) and to the pyrazoline triplet (τ < 9 ns), respectively. The efficiency of the photosensitization process has been evaluated by determination of the corresponding quenching rate constant in each instance. Theoretical calculations support a mechanistic pathway involving a trimethylene radical as intermediate that rapidly evolves to the corresponding cyclopropane derivative. The cyclopropane ring-closure is predicted to be faster than rotation around the C-C bond, thus accounting for the observed stereospecificity.

Original language	English
Pages (from-to)	4906-4911
Number of pages	12
Journal	Journal of Organic Chemistry
Volume	68
Issue number	12
DOIs	https://doi.org/10.1021/jo0342471
Publication status	Published - 13 Jun 2003

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title = "Photolysis of Chiral 1-Pyrazolines to Cyclopropanes: Mechanism and Stereospecificity",

abstract = "The photodenitrogenation of chiral trisubstituted 1-pyrazolines has been studied by laser flash photolysis. These experiments have permitted the detection of two transients that have been assigned, for each pyrazoline, to the trimethylene-type diradical resultant from the extrusion of nitrogen (lifetime τ = 0.1-0.8 μs) and to the pyrazoline triplet (τ < 9 ns), respectively. The efficiency of the photosensitization process has been evaluated by determination of the corresponding quenching rate constant in each instance. Theoretical calculations support a mechanistic pathway involving a trimethylene radical as intermediate that rapidly evolves to the corresponding cyclopropane derivative. The cyclopropane ring-closure is predicted to be faster than rotation around the C-C bond, thus accounting for the observed stereospecificity.",

author = "Elena Muray and Ona Illa and Castillo, {Jos{\'e} A.} and {\'A}ngel {\'A}lvarez-Larena and Bourdelande, {Jos{\'e} L.} and Vicen{\c c} Branchadell and Ortu{\~n}o, {Rosa M.}",

year = "2003",

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doi = "10.1021/jo0342471",

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T1 - Photolysis of Chiral 1-Pyrazolines to Cyclopropanes: Mechanism and Stereospecificity

AU - Muray, Elena

AU - Illa, Ona

AU - Castillo, José A.

AU - Álvarez-Larena, Ángel

AU - Bourdelande, José L.

AU - Branchadell, Vicenç

AU - Ortuño, Rosa M.

PY - 2003/6/13

Y1 - 2003/6/13

N2 - The photodenitrogenation of chiral trisubstituted 1-pyrazolines has been studied by laser flash photolysis. These experiments have permitted the detection of two transients that have been assigned, for each pyrazoline, to the trimethylene-type diradical resultant from the extrusion of nitrogen (lifetime τ = 0.1-0.8 μs) and to the pyrazoline triplet (τ < 9 ns), respectively. The efficiency of the photosensitization process has been evaluated by determination of the corresponding quenching rate constant in each instance. Theoretical calculations support a mechanistic pathway involving a trimethylene radical as intermediate that rapidly evolves to the corresponding cyclopropane derivative. The cyclopropane ring-closure is predicted to be faster than rotation around the C-C bond, thus accounting for the observed stereospecificity.

AB - The photodenitrogenation of chiral trisubstituted 1-pyrazolines has been studied by laser flash photolysis. These experiments have permitted the detection of two transients that have been assigned, for each pyrazoline, to the trimethylene-type diradical resultant from the extrusion of nitrogen (lifetime τ = 0.1-0.8 μs) and to the pyrazoline triplet (τ < 9 ns), respectively. The efficiency of the photosensitization process has been evaluated by determination of the corresponding quenching rate constant in each instance. Theoretical calculations support a mechanistic pathway involving a trimethylene radical as intermediate that rapidly evolves to the corresponding cyclopropane derivative. The cyclopropane ring-closure is predicted to be faster than rotation around the C-C bond, thus accounting for the observed stereospecificity.

U2 - 10.1021/jo0342471

DO - 10.1021/jo0342471

M3 - Article

SN - 0022-3263

VL - 68

SP - 4906

EP - 4911

JO - Journal of Organic Chemistry

JF - Journal of Organic Chemistry

IS - 12

ER -

Photolysis of Chiral 1-Pyrazolines to Cyclopropanes: Mechanism and Stereospecificity

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