Synthese von Heterocyclen, L '). -Synthese von 2,4-Diaryl-5-cyan-l,6-dihydrod-thioxo-3-pyridincarbonsaure-ethylestern aus u-Benzoylzimtsaure-ethylestern Die Umsetzung von a-Benzoylzimtsaure-ethylestern 2 mit Cyanthioacetamid (1) in Methanol/Natriummethanolat fiihrt zu den Natriumsalzen der 2,4-Diaryl-5-cyan-l,2,3,4-tetrahydro-2-hydroxy-6-mercapto-3-pyridincarbonsaure-ethylester 3. Diese konnen zu Methylthio-Derivaten 4 methyliert oder zu Dihydropyridonen 5 dehydratisiert werden. Die Verbindungen 4 werden mittels Nitrosylschwefelsaure zu den entsprechenden aromatischen 2-(Me-thy1thio)pyridinen oxidiert. Andererseits fuhrt eine ahnliche Behandlung der Derivate 5 zwar zu Aromatisierung, aber isoliert werden die Disulfide 6. Reduktion dieser Disulfide ergibt 2-Thiopyridone 7, woraus die zugehorigen 2-Pyridone 9 hergestellt werden konnen. Diese Produkte entstehen auch bei der basischen Hydrolyse von (Methy1thio)pyridinen 8.
In a previous paper in this journal*', we reported on the synthesis of 2-pyridinethiones involving the reaction of cyanothioacetamide (1) with u-benzoylcinnamonitriles from which 4,6-diaryl-1,2-dihydro-2-thioxo-3,S-pyridinedicarbonitriles were obtained. As an extension of this synthesis, we now report on the reaction of 1 with ethyl ct-benzoylcinnamates. This reaction leads to several hitherto unknown 2-pyridinethiones and related compounds.
On treatment of ethyl a-benzoylcinnamates 2 with cyanothioacetamide (1) in ethanol solution and in the presence of sodium methoxide as the basic catalyst, conjugate addition at the double bond of the cinnamates 2 takes place, followed by spontaneous cyclization to give a nitrogen-containing ring. However, neither dehydration nor aromatization takes place and the stable sodium salts 3 are obtained. These species seem to be stabilized by an intramolecular hydrogen bond in the configuration shown, responsible for the remarkable high-field shifts of the 'H signals due to the methyl (6 = 0.4) and methylene group (6 = 3.5) (Table 2) of the equatorial ethoxycarbonyl function, shielded by the two contiguous aryl groups. The 'H NMR spectra of these compounds show also a pair of doublets at about 6 = 4.1 and 2.7 with a coupling constant of 12 Hz, indicating a trans-diaxial configuration of 4-H and 5-H. The hydroxy signal appears as a broad singlet at rather low field (6 N 5.8).
The OH and NH groups give rise to a broad band at 2800-3600 cm-' in the IR spectra,