Reversal of Stereoselectivity in Cycloadditions of Five-Membered Cyclic Nitrones Derived from Hexoses

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Authors	MALATINSKY T. SPISAKOVA M. BABJAK M. DOHANOSOVA J. MAREK Jaromír MONCOL J. FISCHER R.
Year of publication	2017
Type	Article in Periodical
Magazine / Source	European Journal of Organic Chemistry
MU Faculty or unit	Central European Institute of Technology
Citation
Web	https://onlinelibrary.wiley.com/doi/epdf/10.1002/ejoc.201601488
Doi	http://dx.doi.org/10.1002/ejoc.201601488
Keywords	Heterocycles; Nitrones; Carbohydrates; Cycloaddition; Diastereoselectivity
Description	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.
Related projects:	Czech Infrastructure for Integrative Structural Biology