Reactions of azovinylphosphonates with nucleophilic alkenes and heterocycles: synthesis of Tetrahydropyridazine-3-phosphonate and 2-Substituted-1-hydrazonoethylphosphonate derivatives

Transient azovinylphosphonates, generated in situ by base induced dehydrohalogenation of the corresponding 2-bromo- and 2-chloro-acetylphosphonate- tertbutoxycarbonyl hydrazones are intercepted by electron rich alkenes and heterocycles in hetero Diels-Alder reactions, producing tetrahydopyridazine-3-phosphonates or open chain α-hydrazono phosphonates