Preparation of tricyclic imidazopyridines by asymmetric ketone hydrogenation in the presence of RuCl2[(S)-Xyl-P-Phos][(S)-DAIPEN]
作者:Andreas Marc Palmer、Antonio Zanotti-Gerosa、Hans Nedden
DOI:10.1016/j.tetasy.2008.05.013
日期:2008.6
The novel complex RuCl2[(S)-Xyl-P-Phos][(S)-DAIPEN] was identified as a highly active catalyst for the asymmetric reduction of a variety of prochiral ketones possessing an imidazo[1,2-a]pyridine scaffold. The corresponding alcohols were obtained in excellent enantiomeric purities (>96% ee) and served as valuable intermediates for the synthesis of pharmacologically active 7H-8,9-dihydropyrano[2,3-c]imidazo[ 1,2-alpyridines. The complexity of these multi-functional substrates required the development of specific reaction conditions. Whereas the reduction with RuCl2[PP][NN] catalysts (Noyori catalysts) has never been reported to occur under aqueous conditions, in the present case, the use of aqueous isopropanol or tert-butanol was not only tolerated, but also turned out to be beneficial, especially when the reduction was conducted at high substrate to catalyst (S/C) ratios. (C) 2008 Elsevier Ltd. All rights reserved.