Issue 48, 2019

Electronic effects in tautomeric equilibria: the case of chiral imines from d-glucamine and 2-hydroxyacetophenones

Abstract

A one-pot procedure for preparing a series of chiral imines by direct condensation of D-glucamine with 2-hydroxyacetophenones is described. Under conventional acetylation an unexpected mixture of two different peracetylated molecules is obtained, one with an open enamine structure, and the other incorporating an N-acetyl-1,3-oxazolidine into the acyclic skeleton. Surprisingly, both molecules coexist within the crystal's unit cell, as inferred from single-crystal X-ray analysis of a 5-bromo-substituted aryl derivative. Moreover, the 1,3-oxazolidine ring exists as rotational conformers (E,Z) owing to the restricted rotation around the N-acetyl bond. The equilibrium involving imine and enamine structures has been assessed in detail, providing in addition linear free-energy relationships between the tautomerization constants (KT) and the electronic effect of the substituents.

Graphical abstract: Electronic effects in tautomeric equilibria: the case of chiral imines from d-glucamine and 2-hydroxyacetophenones

Supplementary files

Article information

Article type
Paper
Submitted
04 Oct 2019
Accepted
15 Nov 2019
First published
19 Nov 2019

Org. Biomol. Chem., 2019,17, 10209-10222

Electronic effects in tautomeric equilibria: the case of chiral imines from D-glucamine and 2-hydroxyacetophenones

E. Matamoros, P. Cintas, M. E. Light and J. C. Palacios, Org. Biomol. Chem., 2019, 17, 10209 DOI: 10.1039/C9OB02147G

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