Jump to main content
Jump to site search

Issue 72, 2015
Previous Article Next Article

Controlling ring-chain tautomerism through steric hindrance

Author affiliations

Abstract

We have explored the use of steric hindrance for favouring/hindering the tautomerisation of Schiff bases (SB) into tetrahydroquinazolines (TQ) in two systems that derive from the condensation of 2-tosylaminobenzylamine with two different aldehydes: 2,3-dihydroxybenzaldehyde (H2L1SB/H2L1TQ) and N-(3-formylpyridin-2-yl)pivalamide (H2L2SB/H2L2TQ). The four possible ring-chain tautomers were unequivocally characterised by a combination of 1H NMR spectroscopy, infrared spectroscopy, mass spectrometry and elemental analysis. Furthermore, two of the tautomers, H2L1SB and H2L2TQ, have been characterised by X-ray crystallography. Crystal data of E-H2L1SB have revealed the existence of a prototropic ketoenamine–enolimine equilibrium at room temperature that is the cause of the thermochromism of H2L1SB. A firm intramolecular interaction Ohydroxyl–H⋯Nimine hinders the conversion of the chain tautomer H2L1SB into the ring tautomer H2L1TQ. Crystals of H2L2TQ and H2L2TQ·HCCl3 consist of racemic mixtures of their enantiomers, C(R),N(R)-H2L2TQ and C(S),N(S)-H2L2TQ. A terminal pivalamide group prevents the existence of the intramolecular interaction Npivalamide–H⋯Nimine in the chain tautomer H2L2SB, favouring its conversion into the ring tautomer H2L2TQ.

Graphical abstract: Controlling ring-chain tautomerism through steric hindrance

Back to tab navigation

Supplementary files

Article information


Submitted
28 May 2015
Accepted
26 Jun 2015
First published
29 Jun 2015

RSC Adv., 2015,5, 58327-58333
Article type
Paper
Author version available

Controlling ring-chain tautomerism through steric hindrance

A. M. García-Deibe, C. Portela-García, M. Fondo and J. Sanmartín-Matalobos, RSC Adv., 2015, 5, 58327 DOI: 10.1039/C5RA10132H

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.


Social activity

Search articles by author

Spotlight

Advertisements