Iterative Synthesis of 2-Deoxyoligosaccharides Enabled by Stereoselective Visible-Light-Promoted Glycosylation
The photoinitiated intramolecular hydroetherification of alkenols has been used to form C?O bonds, but the intermolecular hydroetherification of alkenes with alcohols remains an unsolved challenge. We herein report the visible-light-promoted 2-deoxyglycosylation of alcohols with glycals. The glycosylation reaction was completed within 2 min in a high quantum yield (?=28.6). This method was suitable for a wide array of substrates and displayed good reaction yields and excellent stereoselectivity. The value of this protocol was further demonstrated by the iterative synthesis of 2-deoxyglycans with α-2-deoxyglycosidic linkages up to a 20-mer in length and digoxin with β-2-deoxyglycosidic linkages. Mechanistic studies indicated that this reaction involved a glycosyl radical cation intermediate and a photoinitiated chain process.
γ-Amino Butyric Acid (GABA) Synthesis Enabled by Copper-Catalyzed Carboamination of Alkenes
γ-Amino butyric acid (GABA) is the chief inhibitory neurotransmitter in the mammalian central nervous system. Many GABA derivatives are used clinically to prevent or treat neurodegenerative diseases. Copper-catalyzed carboamination of alkenes offers an efficient method to fashion the core structure of GABA derivatives from alkenes. In this reaction, acetonitrile serves as the source of the carbon and nitrogen functionalities used to difunctionalize alkenes. Experimental and density functional theory (DFT) studies were carried out to investigate the mechanism of the reaction, and a copper-catalyzed radical-polar crossover mechanism is proposed.
Synthesis of functionalized epoxides by copper-catalyzed alkylative epoxidation of allylic alcohols with alkyl nitriles
A copper-catalyzed oxyalkylation of allylic alcohols using nonactivated alkyl nitriles as reaction partners was developed. A sequence involving generation of an alkyl nitrile radical followed by its addition to a double bond and a copper-mediated formation of C(sp3)-O bond was proposed to account for the reaction outcome. The protocol provided an efficient route to functionalized tri- and tetrasubstituted epoxides via formation of a C(sp3)-C(sp3) and a C(sp3)-O bond with moderate to excellent diastereoselectivity.
Bunescu, Ala,Wang, Qian,Zhu, Jieping
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p. 1890 - 1893
(2015/04/27)
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