Context (archaeology)

Catalysis

Enantioselective synthesis

Composite number

Carbon–carbon bond

Organic synthesis

Biology

Ketone

Materials science

Aldol reaction

Electrophile

Lewis acids and bases

Lewis acid catalysis

Carbon fibers

Paleontology

Combinatorial chemistry

Organic chemistry

Reagent

Organocatalysis

Composite material

Chemistry

Ketene

Nature Chemistry

The chemical synthesis of organic molecules involves, at its very essence, the creation of carbon-carbon bonds. In this context, the aldol reaction is among the most important synthetic methods, and a wide variety of catalytic and stereoselective versions have been reported. However, aldolizations yielding tertiary aldols, which result from the reaction of an enolate with a ketone, are challenging and only a few catalytic asymmetric Mukaiyama aldol reactions with ketones as electrophiles have been described. These methods typically require relatively high catalyst loadings, deliver substandard enantioselectivity or need special reagents or additives. We now report extremely potent catalysts that readily enable the reaction of silyl ketene acetals with a diverse set of ketones to furnish the corresponding tertiary aldol products in excellent yields and enantioselectivities. Parts per million (ppm) levels of catalyst loadings can be routinely used and provide fast and quantitative product formation in high enantiopurity. In situ spectroscopic studies and acidity measurements suggest a silylium ion based, asymmetric counteranion-directed Lewis acid catalysis mechanism.

Approaching sub-ppm-level asymmetric organocatalysis of a highly challenging and scalable carbon–carbon bond forming reaction