尾-Oxygen Effect in the Barton鈥揗cCombie Deoxygenation Reaction: Further Experimental and Theoretical Findings

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• 作者：Alma S谩nchez-Eleuterio ; Jacinto Sandoval-Lira ; Jenny Garc铆a-S谩nchez ; Lorena Monterrosas-P茅rez ; Julio M. Hern谩ndez-P茅rez ; Leticia Quintero ; Fernando Sartillo-Piscil
• 刊名：Journal of Organic Chemistry
• 出版年：2013
• 出版时间：September 20, 2013
• 年：2013
• 卷：78
• 期：18
• 页码：9127-9136
• 全文大小：567K
• 年卷期：v.78,no.18(September 20, 2013)
• ISSN：1520-6904

文摘

The chemistry of (S)-methyl xanthates derived from xylo- and ribo-furanose derivatives in the presence of the stannyl radical is investigated. Xanthate derived from 尾-xylo-furanose affords exclusively a deoxygenated product; whereas, under the same reaction conditions, the 伪-ribo-furanose xanthate derivative produces quantitatively a hemithioacetal compound. We reasoned that in the case of the 尾-xylo-furanose derivative, a favorable 尾-oxygen effect in the Barton鈥揗cCombie deoxygenation reaction is operating where, according to theoretical calculations, unusual molecular orbital interactions (and not strain, as previously proposed) are present. These orbital interactions involve the SOMO (intermediary generated from the stannyl radical addition) with the 蟽* orbital of the bond undergoing cleavage and this with the two C鈥揙 antibonding orbitals anti oriented. Such molecular orbital interactions are not present in the 伪-ribo-furanose; therefore, the 尾-scission is highly delayed, and due to the reversibly nature of the stannyl radical addition, the ribo-furanose xanthate is forced to take an alternative route: the homolytic substitution (S_H2) of the sulfide sulfur by stannyl radical. This radical addition gives the alkoxythiocarbonyl radical, which is trapped by Bu₃SnH before the elimination of carbonyl sulfide; subsequently, radical stannyl addition followed by radical reduction produces the hemithioacetal.