Studies of thieno(3,4-b)pyridines

Heath, D.J., 1989. Studies of thieno(3,4-b)pyridines. PhD, Nottingham Trent University.

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The preparations of 2,3- and 3,2-fused thieno(b)pyridines developed at Trent Polytechnic were applied to the production of 2,4-dioxygenated and 4-oxygenated thieno(3,4-b)-pyridine analogues, from which chloro compounds were made.

The nucleophilic substitution reactions of some chlorothieno(3,4-b)pyridine compounds were found either to be similar to the quinoline analogues or to be anomalous to both the quinoline and 2,3-fused thieno(b)pyridine series. The methoxydechlorination of 2,4-dichlorothieno(3,4-b)pyridine with one-mol equivalent of methoxide, gave both the α- and γ-monosubstituted products under mild conditions. Under identical conditions, 2,4-dichloro-3-methoxycarbonylthieno-(3,4-b)pyridine, gave a mixture of the dimethoxy product and starting material.

The electrophilic substitution reactions of four 2,4-dioxygenated and 4-oxygenated thieno(3,4-b)pyridine compounds were studied. Of these only one reacted smoothly to give a single (bromination) product. The 2,3-fused thieno(b)-pyridine and quinoline analogues of these compounds all react smoothly to give single substitution products.

The 13c n.m.r. spectra of a number of thieno (3,4-b)pyridine compounds were recorded and in most cases resonances were assigned. The information helped in structure determination and preferred keto-enol tautomeric forms were determined. The 2,4-dioxygenated thieno(3,4-b)pyridines prepared exist as the γ-enol, α-keto forms, in line with the other thieno(b)pyridine and quinoline analogues.

Some thieno (3,4-b) pyridine analogues of stable 2,3-fused. thieno(b)pyridine and quinoline compounds were found to be unstable. The lack of stability in the thieno(3,4-b)pyridine series is probably due to the higher energy quinonoid structure in the pyridine ring, compared to the Kekule form found in the other three systems.

The rates of nucleophilic displacement of α- and γ-chlorine atoms in the monochlorinated quinoline and thieno(b)-pyridine compounds were determined. A solvent system was developed which allowed the rates to be determined conveniently and comparisons of the rate constants within each of the systems were made. The activation energy and activation entropy for a few reactions have been calculated.

Item Type: Thesis
Creators: Heath, D.J.
Date: 1989
ISBN: 9781369314007
Divisions: Schools > School of Science and Technology
Record created by: Jeremy Silvester
Date Added: 18 Sep 2020 07:42
Last Modified: 19 Jul 2023 10:21

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