Abstract
In the fine chemical industry, transfer hydrogenation of carbonyl compounds is an important route to selectively form the corresponding allyl alcohol. The Meerwein–Ponndorf–Verley reduction (MPV) is catalyzed by a Lewis acid catalyst and easily oxidizable alcohols serve as hydrogen donor. We successfully used the Zr-based metal-organic framework (MOF) MOF-808-P as MPV-catalyst with isopropyl alcohol as solvent and hydride donor. After only 2 h, 99% yield of cinnamyl alcohol was obtained. The highly active MOF-808-P is also a good catalyst for the selective reduction of more challenging substrates such as R-carvone and β-ionone. Two strategies were successfully used to shift the equilibrium towards the desired allylic alcohol products: (1) evaporation of formed acetone and (2) the use of the more strongly reducing 1-indanol. Carveol yield was increased to >70%. These results highlight the great potential of this recently discovered Zr-MOF as a chemically and thermally stable catalyst.
Highlights
In the fragrance and pharmaceutical industry, allylic alcohols are important intermediates and flavoring compounds [1]
A widespread route to obtaining these allylic alcohols is via the chemoselective reduction of unsaturated aldehydes and ketones
Hydrogen donor and acceptor coordinate simultaneously to the Lewis acidic metal center; via this coordination, the carbonyl group of the substrate is activated for the hydride transfer and the reduction is performed with high selectivity [5]
Summary
In the fragrance and pharmaceutical industry, allylic alcohols are important intermediates and flavoring compounds [1]. A widespread route to obtaining these allylic alcohols is via the chemoselective reduction of unsaturated aldehydes and ketones. This reduction can be performed via hydrogen transfer from oxidizable alcohols catalyzed by a Lewis acid or basic catalyst, a procedure called Meerwein–Ponndorf–Verley reduction (MPV) [2]. MPV reductions are typically performed under mild conditions and with high chemoselectivity because of the low risk of reducing other functional groups or unsaturated C=C-bonds. Hydrogen donor and acceptor coordinate simultaneously to the Lewis acidic metal center; via this coordination, the carbonyl group of the substrate is activated for the hydride transfer and the reduction is performed with high selectivity [5]. To direct the equilibrium towards the desired allylic alcohol, IPA is often used in excess as the solvent of the reaction
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