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The organocatalytic stereoselective alkylation of aldehydes is carried out with the four stable carbocations 1 , 2 , 3 , 4 in the presence of a catalytic amount (20 mol%) of MacMillan imidazolidinones 5 , 6 . In all reactions, lutidine was used as a base. The alkylation reactions are investigated at different temperatures with linear and branched aldehydes. In the case of carbocation tropylium fluoroborate, an interesting reversal of alkylation product configuration was observed, which is driven by entropic effects in the reaction. The absolute configuration of the products obtained is determined by chemical correlation and found to be in general agreement with the model proposed by MacMillan to justify the stereoselectivity obtained in the reactions promoted by catalysts of type 5 , 6 . 相似文献
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Paolo Melchiorre Dr. 《Angewandte Chemie (International ed. in English)》2009,48(8):1360-1363
Following the light: Photoredox catalysis along with aminocatalysis have proved to be the right combination for one of the most challenging asymmetric transformation in organic synthesis: the direct intermolecular α‐alkylation of aldehydes.
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A Brønsted acid catalyzed direct alkylation reaction of aldehydes was described. The 3,5‐dinitrobenzoic acid promoted the reaction between aldehydes and diarylmethanols to afford the corresponding alkylation products with middle to high yields (up to 91% yield). 相似文献
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Enantioselective α‐Alkylation of Aldehydes by Photoredox Organocatalysis: Rapid Access to Pharmacophore Fragments from β‐Cyanoaldehydes 下载免费PDF全文
Eric R. Welin Dr. Alexander A. Warkentin Dr. Jay C. Conrad Prof. Dr. David W. C. MacMillan 《Angewandte Chemie (International ed. in English)》2015,54(33):9668-9672
The combination of photoredox catalysis and enamine catalysis has enabled the development of an enantioselective α‐cyanoalkylation of aldehydes. This synergistic catalysis protocol allows for the coupling of two highly versatile yet orthogonal functionalities, allowing rapid diversification of the oxonitrile products to a wide array of medicinally relevant derivatives and heterocycles. This methodology has also been applied to the total synthesis of the lignan natural product (?)‐bursehernin. 相似文献
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A synergistic catalysis combination of chiral‐at‐metal rhodium complex and amine catalyst was developed for enantioselective alkylation of aldehydes with α,β‐unsaturated 2‐acyl imidazoles. The corresponding adducts were obtained in good yields with excellent enantioselectivities (up to 99% ee). 相似文献
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