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15.1.1.1.4.2.3 Method 3: From Enamines, Aldehydes, and 1,3-Dicarbonyl Compounds (Hantzsch Variation)

DOI: 10.1055/sos-SD-015-00002

Spitzner, D.Science of Synthesis, (20051534.

This method allows the synthesis of unsymmetrically substituted Hantzsch esters (1,4-dihydropyridines) and hence the corresponding unsymmetrically substituted pyridine. Condensation in the presence of tin(IV) chloride induces the oxidation to the pyridines in one pot.[‌147‌] In the case of the condensation of benzaldehyde, ethyl acetoacetate, and ethyl (2E)-3-aminobut-2-enoate (84), followed by acid treatment of the resulting 1,4-dihydropyridine, pyridine 85 is obtained in good overall yield (Scheme 30).[‌42‌,‌148‌] The aldehyde component in the Hantzsch pyridine synthesis can be replaced by an ortho ester. Thus, from enamine 84, ethyl acetoacetate, and triethyl orthoformate, pyridine 86 is formed in 73% yield, besides some byproducts (Scheme 30).[‌149‌]

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