Microwave-Enhanced Asymmetric Transfer Hydrogenation of N-(tert-Butylsulfinyl)imines

Microwave irradiation has considerably enhanced the efficiency of the asymmetric transfer hydrogenation of N-(tert-butylsulfinyl)imines in isopropyl alcohol catalyzed by a ruthenium complex bearing the achiral ligand 2-amino-2-methylpropan-1-ol. In addition to shortening reaction times for the transfer hydrogenation processes to only 30 min, the amounts of ruthenium catalyst and isopropyl alcohol can be considerably reduced in comparison with our previous procedure assisted by conventional heating, which diminishes the environmental impact of this new protocol. This methodology can be applied to aromatic, heteroaromatic and aliphatic N-(tert-butylsulfinyl)ketimines, leading, after desulfinylation, to the expected primary amines in excellent yields and with enantiomeric excesses of up to 96 %.This work was generously supported by the Spanish Ministerio de Ciencia e Innovación (MICINN) (grant numbers CONSOLIDER INGENIO 2010, CSD2007-00006, CTQ2007-65218 and CTQ2011-24151) and the Generalitat Valenciana (PROMETEO/2009/039 and FEDER). O. P. thanks the Spanish Ministerio de Educación for a predoctoral fellowship (grant number AP-2008-00989)

Ether-tethered Ru(ii)/TsDPEN complexes : synthesis and applications to asymmetric transfer hydrogenation

A new type of Ru(II)/TsDPEN catalyst containing an ether-based linking tether has been prepared and shown to exhibit excellent activity in asymmetric transfer hydrogenation reactions of ketones. Related complexes containing a hydroxyl-terminated alkyl chain have also been prepared and tested as asymmetric catalysts. In some cases the activity of the new catalyst type complements that of the closely related alkyl-chain tethered complexes