Sterically Hindered Free-Radicals .21. 1,2- and 1,4-Additions of Diphenylmethyl Radicals to Substituted Acrylonitriles

 
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1993 (EN)
Sterically Hindered Free-Radicals .21. 1,2- and 1,4-Additions of Diphenylmethyl Radicals to Substituted Acrylonitriles (EN)

Zarkadis, A. K. (EN)

Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας (EL)
Zarkadis, A. K. (EN)

Additions of the substituted diphenylmethyl radicals Ar1Ar2CR 2 (R = CMe3, SiMe3, GeMe3, SnMe3, OSiMe3, CF3, CO2Me, CN) to various acrylonitriles CH2 = C(X)CN 3 (X = SMe, SiPr, StBu, OAc, OSiMe3, OSiEt3, OMe, OEt) lead to 1,2-5 or 1,4-adducts 6 (ketenimines), depending mainly on the steric hindrance by the substituents R and X. Bulky substituents like tBu in 2 and tBuS in the acrylonitrile favour the formation of the extended and nearly strainless ketenimine system 6 (1,4-adduct); smaller substituents like OSiMe3 (radical 2) and SMe, OAc, OSiMe3, OSiEt3, OMe, OEt (acrylonitrile) allow isolation of the sterically crowded 1,2-adducts. Substituents of intermediate bulkiness like CF3 (radical 2) and SiPr (acrylonitrile) give a mixture of 1,2-adducts (6cb,hb) and dimers 7 of the adduct radicals 4 (7cb,hb). The voluminous tBu group directly bound to the olefin (3j,k) prevents addition. The latter is generally reversible, and the various adducts 5, 6, or 7 dissociate to the adduct radicals 4 and/or fragment to the initial radicals 2 at temperatures which reflect the steric strains of the corresponding substituents R, X. The complete inertness, even toward the electron-rich olefin 3i, of the electrophilic alpha-carbonyl-substituted radicals 2q-s (R = CHO, COMe, COPh) in the above additions is discussed. Additions of the radicals 2a-c,f,i,n,o to the conjugated olefin 3n are described and are in accordance with the conclusion that steric effects predominate in adduct formation, whereas electronic effects are of distinct but minor importance. (EN)

radical additions (EN)

Πανεπιστήμιο Ιωαννίνων (EL)
University of Ioannina (EN)

Chemische Berichte-Recueil (EN)

English

1993

<Go to ISI>://A1993LF23000017



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