Synthesis of poly-functionalized pyrazoles and pyridazines from nitrobutadienes: an interesting dichotomy of practical relevance

The initial ring-opening of 3-nitrothiophene and further structural modifications lead to nitrobutadienic building-blocks whose synthetic usefulness in the field of heterocycles has been widely demonstrated. As a further example, the Michael addition of a hydrazone anion to the nitrovinyl moiety of nitrobutadienes generates 1,2-diazaheterocycles as the final result of an overall MIRC process. Depending on the nature of the substituents on the Michael-type acceptor and on the hydrazono nucleophile, an interesting dichotomy is observed that leads to either five-member or six-member N-heterocycles with complete selectivity. The results obtained appear to be both of mechanistic and synthetic interest e.g., in the field of heterocycles endowed with potential pharmacological/biological activity.

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