In my work for bachelor’s degree, 1-cyano-4-oxo-4H-quinolizine-3-diazonium tetrafluoroborate was synthesized from 2-(pyridin-2-yl)carbonitrile and methyl (2Z)-2-benzamido-3-(dimethylamino)prop-2-enoate as starting compounds. The synthesis was carried out first on a smaller 10 mmol scale and then on a bigger 30 mmol scale. The reaction between enaminone and the derivative of pyridine was a cyclocondensation reaction between 2-(pyridin-2-yl)carbonitrile, which acted as a dinucleophile, and methyl (2Z)-2-benzamido-3-(dimethylamino)prop-2-enoate, which acted as a dielectrophile. In this reaction, methanol and dimethylamine were the by-products of the cyclocondensation and N-(1-cyano-4-oxo-4H-quinolizin-3-yl)benzamide was formed as the main product. Enaminone, with which the derivative of 4H-quinolizin-4-one was formed, also contained the protected amine group in a form of a benzamide, which stayed bound in the bicyclic product at the position 3. The protected amino group was transformed with hydrochloric acid into the free amine and the protecting group was removed in a form of benzoic acid. In the last step of synthesis, the free amine, that was formed in the previous step, was converted into a diazonium salt using NaNO2 and HBF4. Tetrafluoroborate was used as an anion to stabilize the diazonium cation and a stable diazonium salt was obtained. This diazonium salt can be further used for the reactions of azo coupling or for introducing different functionalities to the 4H-quinolizin-4-one ring.
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