Reversal of Stereoselectivity in Cycloadditions of Five-Membered Cyclic Nitrones Derived from Hexoses
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- 作者：Tomá ; š Malatinský ; Má ; ria Spišá ; ková ; Matej Babjak ; Jana Dohá ; ňošová ; Jaromí ; r Marek ; Já ; n Moncol and Ró ; bert Fischer
- 刊名：European Journal of Organic Chemistry
- 出版年：2017
- 出版时间：February 10, 2017
- 年：2017
- 卷：2017
- 期：6
- 页码：1086-1098
- 全文大小：2362K
- ISSN：1099-0690
文摘
Two five-membered cyclic nitrones derived from hexoses, a newly synthesized d-allo-configured nitrone and an already known d-talo-configured nitrone, have been examined in 1,3-dipolar cycloaddition reactions with vinyl acetate, allyl benzoate, methyl acrylate, acrylonitrile, and vinylene carbonate. The reactions of the d-allo-configured nitrone proceeded preferentially through the expected exo-anti transition state, but all the cycloadditions of the d-talo-configured nitrone surprisingly showed high exo-syn selectivity. This reversal of stereoselectivity has been explained by 3D analysis of the preferred conformations of the nitrones, obtained from X-ray data. The structures were further inspected using CONFLEX, PM5, and DFT calculations. All these methods revealed that the dioxolane substituents attached to C-5 of both nitrones had opposite spatial locations.