Chiral imidazolidinone and proline-derived surface modifiers for the Pt-catalysed asymmetric hydrogenation of activated ketones

• Modular nature of the modifier allows for the rapid generation of structural diversity.
• High enantioselectivities using parameters optimised for the Pt/cinchonidine system.
• The substitution of OH → F is accompanied by a significant improvement in enantioselectivity.

A series of imidazolidinone and proline derivatives have been synthesised and tested with regard to their suitability for the chiral modification of platinum used for the asymmetric hydrogenation of activated ketones. Hydrogenations of ketopantolactone (KPL), methyl benzoylformate (MBF) and trifluoroacetophenone (TFAP) performed at low hydrogen pressures (1 and 10 bar) were selected as test reactions. With some of these synthethic modifiers, encouraging levels of enantioselectivity were achieved (up to 73.5:26.5 e.r.) without optimisation of the reaction conditions. Moreover, performance enhancement of l-proline derived-modifiers, as a consequence of molecular editing with fluorine, was found to be significant (OH → F, Δee up to 23%) contributing to the growing interest in modulating catalyst performance by fluorine introduction.

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