Читать книгу Catalytic Asymmetric Synthesis - Группа авторов - Страница 38

Rovis reported a domino Michael/benzoin reaction of 1,3‐diketones and α,β‐unsaturated aldehydes by using a combination of diarylprolinol silyl ether and N‐heterocyclic carbene catalyst (Eq. 1.37) [67]. This is a formal [3+2] cycloaddition reaction that affords highly functionalized cyclopentanone derivatives with excellent enantioselectivity. When only diarylprolinol silyl ether was employed as a single catalyst, first Michael reaction proceeded to afford the Michael product with lower enantioselectivity, because of the retro‐Michael reaction. A combined use of the two catalysts not only provided the formal [3+2] cycloaddition products but also realized excellent enantioselectivity.

(1.37)

Luo reported a unique two‐catalyst cooperative system of a chiral primary amine and a ketone for the asymmetric α‐hydroxylation of β‐ketocarbonyls with H₂O₂ (Eq. 1.38) [68]. A chiral primary amine not only reacts with β‐ketocarbonyl to generate an enamine, it also reacts with 2,2,2‐trifluoroacetophenone to generate a chiral ketimine, which reacts further with H₂O₂ to afford an oxaziridine intermediate. The chiral enamine–chiral oxaziridine coupling provided α‐hydroxylated β‐ketocarbonyls in excellent yield with excellent enantioselectivity.

(1.38)