Abstract
Sulphur analogues of uracil and thymine have been prepased, in which the N1 atom of the pyrimidine base has
been replaced by a sulphur atom. A number of general
synthetic methods are described for the synthesis of these 1,3-thiazines. The uracil analogues were prepared from the
related 2-thio-1,3-thiazines, by acid hydrolysis of
the 2-alkylthio derivative. 3,4-Dihydro-4-oxo-2-thio-2H-1,3-thiazine,
its N-methyl and N-ethyl derivatives were obtained by cyclization of the
addition compound resulting from the reaction of propiolic acid and the
appropriate dithiocarbamic acid. The generality of
this reaction, when propiolic acid is replaced with other acetylenic
acids or their related esters, is discussed. The crystalline addition compounds
obtained from dithiocarbamic acid and either
propiolic acid or methyl propiolate were all shown by
p.m.r, spectroscopy to have cis stereo-chemistry. The thymine analogues were prepared by an
alternative route, which utilized the intramolecular cyclization of S-ethyl-N-(β-methoxymethacryloyl)dithiocarbamate
to form 2-ethylthio-6-methyl-4-oxo-4H-1,3-thiazine,
followed by acid hydrolysis of the 2-ethylthio group.
Related intramolecular cyclization reactions of N-acyl-dithiocarbamates
formed the 5-acetyl-, the 5-cyano-6-methyl-, the 5-cyano-6-ethyl-, and the
6-methyl-2-ethylthio-1,3-thiazine derivatives. A
third approach involved the successful acid catalysed ring-opening-ring-
closure of a. 4-oxo-2-thio-1,3-oxazine to the
isomeric 2,4-dioxo-1,3-thiazine.
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