Ligand-Assisted Acyl Migration in Au-Catalyzed Isomerization of Propargylic Ester to Diketone: A DFT Study

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• 作者：Animesh Ghosh ; Atanu Basak ; Kuheli Chakrabarty ; Boyli Ghosh ; Gourab Kanti Das
• 刊名：Journal of Organic Chemistry
• 出版年：2014
• 出版时间：June 20, 2014
• 年：2014
• 卷：79
• 期：12
• 页码：5652-5663
• 全文大小：827K
• 年卷期：v.79,no.12(June 20, 2014)
• ISSN：1520-6904

文摘

Gold-catalyzed isomerization of propargylic ester to a diketone derivative is a fascinating example for the generation of the C鈥揅 bond in organoaurate chemistry as it is one of the few reactions that exploit the nucleophilicity of organoaurates to a migrating acyl group. The proposed mechanistic pathway, involving the formation of a four-membered intermediate, has never been substantiated by any theoretical or experimental evidence. Detailed theoretical calculation suggests that the formation of an alkylideneoxoniumcyclobutene intermediate is highly unlikely. Instead, an acyl migration, assisted by the chlorine ligand in the square planar geometry of metal complex offers an alternative mechanism that can justify the reasonable activation barrier and the associated stereochemical feature involved in the reaction. The initial mandatory steps of the catalytic process such as allene formation (af) and rotamerization of allene-bound gold complex (ra) are found to be quite facile. However, the final step, acyl migration (am), that takes place through the formation of an intermediate with C鈥揅l bond, acts as the rate-determining step of the reaction. The mechanism also justifies the lack of sufficient activity of Au(I) salt to catalyze the isomerization process.