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Título
On the Mechanism and Kinetics of Radical Reactions of Epoxyketones and Epoxynitriles Induced by Titanocene Chloride
Autor(es)
Materia
Reacciones químicas
Radicales (Química)
Química orgánica
Clasificación UNESCO
2306 Química Orgánica
Fecha de publicación
2007
Citación
Fernández Mateos, A., Herrero Teijón, P., Mateos Burón, L., Rabanedo Clemente, R. & Rubio González, R. (2007). On the Mechanism and Kinetics of Radical Reactions of Epoxyketones and Epoxynitriles Induced by Titanocene Chloride. The Journal of Organic Chemistry, 72(26), 9973-9982. https://doi.org/10.1021/jo701497e
Resumen
[EN]The reactions of a series of epoxynitriles and epoxyketones induced by titanocene chloride have been
studied. The kinetics of the decyanogenation of β,γ-epoxynitriles with Ti(III) corresponds to a radical
reaction (k25 ≈ 106 s-1), as demonstrated by competition experiments with H-transfer from 1,4-
cyclohexadiene (1,4-CHD) or PhSH or conjugate addition to acrylonitrile. The 5-exo cyclization onto
nitrile induced by Ti(III) is a radical reaction (k25 ≈ 107 s-1) as seen in competition experiments with
H-transfer from PhSH or the titanocene-water complex. The iminyl or alkoxyl radicals generated by
5-exo cyclization onto nitriles or ketones only undergo a reduction with Ti(III). This reaction overwhelms
any alternative process, such as tandem cyclization onto alkenes or β-scission. Iminyl radicals generated
by 4-exo cyclizations onto nitriles undergo reduction with Ti(III) and β-scission reaction in a ratio of
96:4 when the R-substituent is CN. Alkoxyl radicals from 4-exo cyclizations onto ketone carbonyls undergo
reduction with Ti(III) and β-scission in a ratio of 60:40 when the R-substituent is COOR. In nearly all
the reactions studied, the role of Ti(III) is triple: a radical initiator (homolytic cleavage of oxirane), a
Lewis acid (coordination to CN or CdO), and a terminator (reduction of iminyl or alkoxyl radicals).
URI
ISSN
0022-3263
DOI
10.1021/jo701497e
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