title: Titanium-catalyzed reductive umpolung reactions with a metal-free terminal reducing agent.
abstract: A new method for titanium-catalyzed reductive umpolung reactions is reported that overcomes the traditional requirement for a stoichiometric metallic reductant. With N,N'-disilylated tetramethyldihydropyrazine as a potent organic reducing agent, reductive carbonyl-nitrile, enone-acrylonitrile and pinacol coupling reactions can be achieved in good yields and stereoselectivities. [Cp2TiI2] is a superior catalyst to [Cp2TiCl2], which is rationalized by a faster generation of the active catalyst [Cp2TiI]. A mechanism is proposed that is in agreement with the experimental results.
authors.affiliation: Institut für Organische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstraße 21, 79104 Freiburg (Germany), Fax: (+49) 761-203-8715.
authors.forename: Georg
authors.initials: G
authors.lastname: Frey
authors.forename: J Niklas
authors.initials: JN
authors.lastname: Hausmann
authors.forename: Jan
authors.initials: J
authors.lastname: Streuff
keywords: homogeneous catalysis; radicals; reductive coupling; titanium; umpolung