Mechanistic Studies of Highly Enantio- and Diastereoselective Aza-Petasis鈥揊errier Rearrangement Catalyzed by Chiral Phosphoric Acid

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• 作者：Masahiro Terada ; Takazumi Komuro ; Yasunori Toda ; Toshinobu Korenaga
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：May 14, 2014
• 年：2014
• 卷：136
• 期：19
• 页码：7044-7057
• 全文大小：814K
• 年卷期：v.136,no.19(May 14, 2014)
• ISSN：1520-5126

文摘

The precise mechanism of the highly anti- and enantioselective aza-Petasis鈥揊errier (APF) rearrangement of hemiaminal vinyl ethers catalyzed by a chiral phosphoric acid was investigated by undertaking experimental and theoretical studies. The APF rearrangement is characterized by the following unique mechanistic features: (i) efficient optical kinetic resolution of the starting racemic hemiaminal vinyl ether, (ii) enantioconvergent process from racemic hemiaminal vinyl ethers to optically active 尾-amino aldehyde products, and (iii) anomalous temperature effects on the enantioselectivity (enantioselectivity increases as reaction temperature increases). The following experiments were conducted to elucidate the unique mechanistic features as well as to uncover the overall scheme of the present rearrangement: (A) X-ray crystallographic analysis of the recovered hemiaminal vinyl ether to determine its absolute configuration, (B) rearrangements of enantiomerically pure hemiaminal vinyl ethers to validate the stereochemical relationship between the hemiaminal vinyl ethers and 尾-amino aldehydes, (C) theoretical studies on the transition states of the C鈥揙 bond cleavage and C鈥揅 bond formation steps to gain an insight into the optical kinetic resolution of the hemiaminal vinyl ether and the origin of the stereoselectivity, as well as to elucidate the overall scheme of the present rearrangement, and (D) crossover experiments of two hemiaminal vinyl ethers having different vinyl ether and aliphatic substituents to comprehend the mechanism of the anomalous temperature effect and the enantioconvergent process. The results of experiments and theoretical studies fully support the proposed mechanism of the present anti- and enantioselective APF rearrangement.