2 research outputs found
On the Mechanism and Kinetics of Radical Reactions of Epoxyketones and Epoxynitriles Induced by Titanocene Chloride
[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)
Reacciones radicalarias de epoxicetonas insaturadas inducidas por titanoceno
[ES]Tesis doctoral sobre Reacciones radicalarias de epoxicetonas insaturadas inducidas por titanoceno, perteneciente al departamento de química orgánica[EN]Doctoral Thesis on the radical reactions induced by unsaturated titanocene epoxicetonas, from the organic chemistry´s departamen