Ruthenium-Catalyzed Transfer Hydrogenation of the Vinyl Fragment in Heterocyclopentadienes

A highly selective method has been developed for the catalytic transfer hydrogenation of the vinyl group in a number of five-membered heteroarene derivatives. The key achievement is the use of [RuCl 2 ( p -cymene] 2 as catalyst, which provides exceptional chemoselectivity while suppressing undesirable decomposition of the heteroaromatic ring and its overreduction. Optimization of the catalytic system has been performed to determine conditions for the synthesis of the target unsaturated analogues in high yields. The structure and purity of the synthesized compounds have been confirmed by GC/MS and NMR spectroscopy. The proposed methodology opens new ways for the selective reduction of complex heterocyclic compounds that are of significant interest for pharmacological studies.