A catalytic asymmetric nucleophilic addition of tertiary carbon nucleophiles to 2 H-azirines was established in the presence of the chiral N,N'-dioxide/Cu complex. Various chiral aziridines with vicinal tetrasubstituted stereocenters were obtained in high yields with excellent diastereoselectivities and enantioselectivities. Moreover, on the basis of the control experiments, X-ray structures of the products, and catalyst, a possible transition state was proposed to explain the stereoselectivity.
An efficient asymmetric vinylogous Michael−aldol domino reaction between α-arylidene pyrazolinones and β,γunsaturated-α-ketoesters catalyzed by a chiral N,N′-dioxide-Sc III complex in aqueous media has been established. A variety of spirocyclohexene pyrazolones with three stereocenters including vicinal tetrasubstituted stereocenters were obtained in excellent yields with good diastereoselectivities and enantioselectivities. A retro-aldol process was observed, which led to epimerization at the spirocyclic quaternary carbon center.
The first catalytic asymmetric multiple vinylogous addition reactions initiated by Meinwald rearrangement of vinyl epoxides were realized by employing chiral N,N′‐dioxide/ScIII complex catalysts. The vinyl epoxides, as masked β,γ‐unsaturated aldehydes, via direct vinylogous additions with isatins, 2‐alkenoylpyridines or methyleneindolinones, provided a facile and efficient way for the synthesis of chiral 3‐hydroxy‐3‐substituted oxindoles, α,β‐unsaturated aldehydes and spiro‐cyclohexene indolinones, respectively with high efficiency and stereoselectivity. The control experiments and kinetic studies revealed that the Lewis acid acted as dual‐tasking catalyst, controlling the initial rearrangement to match subsequent enantioselective vinylogous addition reactions. A catalytic cycle with a possible transition model was proposed to illustrate the reaction mechanism.
A highly enantioselective 1,3-dipolar cycloaddition of meso-diaziridines with chalcones was realized by utilizing the Sc III −N,N′-dioxide complex as the catalyst. In this transformation, the 1,3-dipole intermediates generated from the C−N bond cleavage of diaziridine were trapped by chiral N,N′-dioxide/scandium(III) complex activated chalcones to undergo enantioselective 1,3-dipolar cycloaddition. A range of chiral 1,5-diazabicylo[3.3.0]octane derivatives were readily synthesized in good yields with high diastereo-and enantioselectivities.
Catalytic asymmetric ene-type reactions of vinylogous hydrazone with isatins, α-ketoester, imines and aldehydes were accomplished which gave an environmentally friendly, straightforward approach to afford bioactive chiral α-methylene-γ-butyrolactone derivatives.
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