What Is Compound 50?

Compound 50, like its known analogue 3, involves an α,β-unsaturated ketone, an acid-sensitive reactant, which prevents its direct synthesis in presence of protic solvents by refluxing. Despite of this characteristic, 50 was formed smoothly in 5 minutes by grinding chemistry, solely as E-isomer, without any evidence of decomposition after 1H and 13C MNR analysis. This synthetic approach provides easy access to such α,β-unsaturated N-acylhydrazones, which are building blocks in the synthesis of nitrogen-containing heterocycles of importance in both medicinal and synthetic chemistry. Finally, the last example of this work analyses the reaction between a 3,4-dichlorobenzohydrazide and isatin, which gives rise to the hydrazone 51 (Table 3, Entry 18).
Unlike all others representative compounds studied here, hydrazone 51 has its stereochemistry controlled by intramolecular interactions instead of steric factors. Despite isatin’s lack of steric requirements around its carbonyl functionality, its hydrazone derivatives exist only as Z-isomers because of the formation of an intramolecular hydrogen bond between de (–NH–) group of the acyclic chain and the oxygen of the isatin’s (–NHCO–)