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MacMillan reported α‐trifluoromethylation (Eq. 1.39) [70], α‐arylation (Eq. 1.40) [71], and α‐vinylation [72] of aldehydes with iodonium salts catalyzed by a combined use of MacMillan’s catalyst and copper catalyst. In the α‐trifluoromethylation reaction, Togni’s reagent is employed as CF₃ source. In the α‐arylation reaction, Cu(I) reacts with diaryliodonium salts to generate aryl‐Cu(III) species, which react with an enamine to generate η¹ iminium organocopper species. Reductive elimination afforded an α‐arylated product, and excellent enantioselectivity was obtained.

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Cordova reported an α‐allylation of an aldehyde with an allyl acetate catalyzed by a combination of diphenylprolinol silyl ether and Pd catalyst (Eq. 1.41). A π‐allyl complex would be generated from allyl acetate and Pd(PPh₃)₄, which reacts with a chiral enamine generated from an aldehyde and organocatalyst [73]. Excellent enantioselectivity was obtained.

(1.41)

Cozzi reported an asymmetric allylation reaction of an aldehyde and an allyl alcohol catalyzed by a combination of MacMillan’s catalyst and a Lewis acid such as InBr₃ (Eq. 1.42) [74]. This is an S_N1‐type reaction, and the chiral enamine, which is generated from an aldehyde and MacMillan’s catalyst, reacts with an allylic carbenium ion, which is generated from an allyl alcohol and InBr₃ to afford the product after hydrolysis.

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Dixon reported an asymmetric carbocyclization of aldehyde‐linked allene by a combined use of diarylprolinol silyl ether and Pd(OAc)₂ to afford a substituted cyclopentanecarbaldehyde with good enantioselectivity (Eq. 1.43) [75]. The organocatalyst reacts with an aldehyde to generate a chiral enamine, which reacts with allene activated by Pd(II).

(1.43)

Gong reported that diphenylprolinol/Pd(II) cooperative catalysis has enabled a highly enantioselective addition of cyclic ketones to unactivated alkenes (Eq. 1.44) [76]. The reaction includes amide‐directed, regioselective activation of alkenes by Pd(II) and enhancing the nucleophilicity of α‐carbon of the ketones by enamine catalysis, which provides the γ‐addition products with good to high yields and efficient stereochemical control.

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Jia reported an enantioselective α‐arylative desymmetrization of cyclohexanones using Pd(OAc)₂ and proline as a chiral amine catalyst (Eq. 1.45) [77]. Morphan derivatives bearing α‐carbonyl tertiary stereocenters were produced in good yields with excellent enantioselectivities. The generated enamine reacts with Ar‐Pd‐X, and β‐hydride elimination affords another enamine, which is hydrolyzed to provide the product (Scheme 1.5).

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Scheme 1.5. The reaction mechanism.

Nishibayashi reported an enantioselective propargylic alkylation of propargylic alcohols with aldehydes in the presence of a thiolate‐bridged diruthenium complex and diarylprolinol silyl ether as a co‐catalyst to afford the corresponding propargylic alkylated products in excellent yields with high enantioselectivity (Eq. 1.46) [78]. This is a new type of enantioselective propargylic substitution reaction, wherein the chiral enamines react with the ruthenium–allenylidene complexes, where both the transition metal catalyst (ruthenium complex) and organocatalyst (secondary amine) activate propargylic alcohols and aldehydes, respectively, and cooperatively.

(1.46)