Chemistry - A European Journal p. 5693 - 5696 (2015)
Update date:2022-07-29
Topics:
Frey, Georg
Hausmann, J. Niklas
Streuff, Jan
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. Replacing zinc: A protocol for titanium(III)-catalyzed reductive umpolung reactions is presented that enables the title reactions in the presence of an N,N′-disilylated tetramethyldihydropyrazine as an organic sacrificial reducing agent. It is successfully applied to carbonyl-nitrile, enone-acrylonitrile and pinacol coupling reactions. A remarkable effect of the titanocene counterion renders titanocene diiodide a superior catalyst.
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