The first enantioselective direct cross-aldol reaction of α-keto amides with aldehydes, mediated by a bifunctional ureidopeptide-based Brønsted base catalyst, is described. The appropriate combination of a tertiary amine base and an aminal, and urea hydrogen-bond donor groups in the catalyst structure promoted the exclusive generation of the α-keto amide enolate which reacted with either non-enolizable or enolizable aldehydes to produce highly enantioenriched polyoxygenated aldol adducts without side-products resulting from dehydration, α-keto amide self-condensation, aldehyde enolization, and isotetronic acid formation.
The first enantioselective direct cross-aldol reaction of a-keto amides with aldehydes,m ediated by ab ifunctional ureidopeptide-based Brønsted base catalyst, is described. The appropriate combination of at ertiary amine base and an aminal, and urea hydrogen-bond donor groups in the catalyst structure promoted the exclusive generation of the a-keto amide enolate whichr eacted with either non-enolizable or enolizable aldehydes to produce highly enantioenriched polyoxygenated aldol adducts without side-products resulting from dehydration, a-keto amide self-condensation, aldehyde enolization, and isotetronic acid formation. Scheme 1. Cross-aldol reactions of 1,2-dicarbonyl compounds. BB = Brønsted base, Tf = trifluoromethanesulfonyl.
The potential of β-alkoxy α-keto amides as pronucleophiles in the enantioselective Mannich type reaction with p-nosyl imines is presented. The proper combination of β-alkoxy α-keto amides and a squaramide-based Brønsted base catalyst produced highly enantioenriched Mannich adducts, which may be transformed into functionalized amino diols.
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