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

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18 Citations (Scopus)


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 languageEnglish
Pages (from-to)4906-4911
Number of pages12
JournalJournal of Organic Chemistry
Issue number12
Publication statusPublished - 13 Jun 2003


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