Electronic effects in tautomeric equilibria: the case of chiral imines from d-glucamine and 2-hydroxyacetophenones.
Org Biomol Chem
; 17(48): 10209-10222, 2019 12 28.
Article
em En
| MEDLINE
| ID: mdl-31774417
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.
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MEDLINE
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En
Ano de publicação:
2019
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Article