title: Key role of Ti(IV) in the selective radical-radical cross-coupling mediated by the Ingold-Fischer effect.
abstract: We report an innovative approach for the selective synthesis of polyfunctional derivatives by cross-combination of different radicals generated under mild conditions. The coordinating effect of Ti(IV) plays a key role in the reaction mechanism: due to its chelating action on the hydroxyl groups, it promotes the homolytic C-C bond cleavage of alpha,beta-dihydroxy ketones by enhancing the captodative effect and the consequent stabilization of the corresponding alpha-hydroxy-alpha-carbonyl radicals. When these radicals are generated in the presence of stoichiometric amounts of TiCl(4) and 2,2'-azo-bis-isobutyronitrile (AIBN) is employed as a source of alpha-cyanoisopropyl radicals, the selective radical-radical cross-coupling is observed, affording the corresponding beta-hydroxynitriles in high yields. This innovative methodology allows application of the well-known Ingold-Fischer effect to a wider range of stabilized carbon-centered radicals, whose formation derives from the chelating action of Ti(IV).
authors.affiliation: Dipartimento di Chimica, Materiali e Ingegneria Chimica "G. Natta", Politecnico di Milano, via Mancinelli 7, I-20131 Milano, Italy.
authors.forename: Raffaele
authors.initials: R
authors.lastname: Spaccini
authors.forename: Nadia
authors.initials: N
authors.lastname: Pastori
authors.forename: Angelo
authors.initials: A
authors.lastname: Clerici
authors.forename: Carlo
authors.initials: C
authors.lastname: Punta
authors.forename: Ombretta
authors.initials: O
authors.lastname: Porta