Control of chirality by cations in confined spaces: Photooxidation of enecarbamates inside zeolite supercages

J. Sivaguru, Hideaki Saito, Marissa R. Solomon, Lakshmi S. Kaanumalle, Thomas Poon, Steffen Jockusch, Waldemar Adam, V. Ramamurthy, Yoshihisa Inoue, Nicholas J. Turro

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19 Scopus citations

Abstract

On photooxygenation of the optically active Z/E enecarbamates 1 (X = i-Pr) and 2 (X = Me) equipped with the oxazolidinone chiral auxiliary in methylene-blue (MB)-incorporated, alkali-metal (M = Li, Na, K, Cs, Rb), exchanged Y-type zeolites (MY-MB), oxidative cleavage of the alkenyl functionality releases the enantiomerically enriched methyldesoxybenzoin (MDB) product. The extent (% ee) and/or the sense (R or S) of the stereoselectivity in the formation of the MDB product depends on the choice of the alkyl substiuent (i-Pr or Me) at the C-4 position of the oxazolidinone chiral auxiliary, the Z/E configuration of the alkene functionality in the enecarbamates, and the type of alkali metal in the zeolite. Most significantly - the highlight of this study - is the reversed sense (R or S) in the stereoselection when the photooxygenation is run in CDCl3 solution versus inside the MY-MB zeolite. As a mechanistic rationale for this novel stereochemical behavior, we propose the combined action of spatial confinement and metal-ion coordination (assessed by density-functional calculations) of the substrate within the zeolite supercage, both of which greatly reduce the freedom of the substrate and entropically manipulate the stereochemical outcome.

Original languageEnglish (US)
Pages (from-to)123-131
Number of pages9
JournalPhotochemistry and Photobiology
Volume82
Issue number1
DOIs
StatePublished - Jan 1 2006

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry

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    Sivaguru, J., Saito, H., Solomon, M. R., Kaanumalle, L. S., Poon, T., Jockusch, S., Adam, W., Ramamurthy, V., Inoue, Y., & Turro, N. J. (2006). Control of chirality by cations in confined spaces: Photooxidation of enecarbamates inside zeolite supercages. Photochemistry and Photobiology, 82(1), 123-131. https://doi.org/10.1562/2005-06-15-RA-573