The synthesis of medium sized heterocycles remains a synthetic challenge mainly due to the unfavorable energetics for forming such ring systems. We recently discovered a highly efficient method for generating 7, 8, and 9-member diaza heterocycles from reaction of diketene acetone adduct and diamines under solvent-free conditions. The reaction was highly intriguing due to its high efficiency, atom economy, green reaction conditions, simplified product purification, and readily available starting materials.  The reaction sequence begins with a retro-Diels-Alder reaction to generate diketene, which undergoes nucleophilic attack by diamines followed by cyclization via an imine condensation reaction. Overall isolated yields were >95% for all three heterocycles.

Extraordinarily efficient synthesis of medium-ring diaza heterocycles from diketene-acetone adduct and diamines

247th National Meeting (2014)

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