Tuning diastereoselectivity with the solvent: the asymmetric hydrogenation of simple and functionalized 1,3-diketones with ruthenium(amidophosphine-phosphinite) catalysts

Spectacular solvent effects in the asymmetric hydrogenation of methyl 3,5-dioxohexanoate (3) and 2,4-pentanedione (5) have been observed using Ru[(S)-Ph,Ph-oxoProNOP]X-2 complexes (X = eta(3)-C4H7, IIa; CF3CO2, IIb; (R)-MTPA, IIc) as catalyst precursors. beta-Diketones 3 and 5 are respectively reduced to the corresponding beta-diols 4 and 6. In both cases, an almost complete reversal in the diastereoselectivity of the reaction is observed when changing the solvent from CH2Cl2 (syn-4 in up to 92% de; meso-6 in up to 84% de) to a 1 : 1 CH2Cl2-CH3OH mixture (anti-4 and anti-6 in up to 84% de). The extent of this solvent effect is much less marked with Ru-atropisomeric diphosphine catalysts.