Allylic alcohols and chiral alcohols are abundant in natural sources such as essential oil, and widely utilized as starting materials and major components in food, fragrance, biocides and pharmaceutical industries. Herein, we report the first Ru-catalysed  asymmetric transfer hydrogenation (ATH) of prochiral allylic alcohols to produce chiral alcohols in excellent enantioselectivity and high yield. This new reaction is much safer, more economical and environmentally friendly for the asymmetric reduction of allylic alcohols compared with high-pressure gaseous hydrogenation. The reaction provides the alcohols with the same chirality as the gaseous hydrogenation reaction with comparable yield and ee. The mechanism studies through several deuterium-labeled experiments indicate a new reaction pathway that the ATH reaction occurs via tandem enantioselective isomerization-transfer hydrogenation process, which is different from the mechanism of gaseous hydrogenation. The asymmetric induction step occurs during the Ru-assisted 1,3-hydrogen shift isomerization through enal intermediate prior to transfer hydrogenation. Reaction conditions can be optimized using chiral ruthenium complexes.

Mechanism studies of Ru-catalysed asymmetric transfer hydrogenation of allylic alcohols

244th National Meeting (2012)

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