Diethyl hydrazodicarboxylate

Alkyl- and aryl carbodiimides can be prepared under mild conditions from thioureas with diethyl azodicarboxylate/triphenylphosphine (Mitsunobu reagent), typically in yields of around 80% the by-products are triphenylphosphine sulfide and diethyl hydrazodicarboxylate [1278]. The active intermediate in this system is the betaine 1739, which is formed from diethyl azodicarboxylate (DEAD) and triphenylphosphine. Driven by its charge distribution and its chalcogenophilicity, 1739 reacts with the thiourea 1740 to form the P,S bond in 1741. This energy-rich molecule stabilizes by decomposition into three molecules, namely the two byproducts, triphenylphosphine sulfide and diethyl hydrazodicarboxylate, and the desired carbodiimide 1699. Diphenylcarbodiimide 1699 (R = R = Ph) was prepared from N,N -diphenylthiourea 1740 (R = R = Ph) with DEAD and triphenylphosphine in 65% yield [1278]. 

Dehydrogenation and Aromatization. Dihydropyridines can be aromatized by dilute nitric and sulfuric acid (eq 18). Diethyl hydrazodicarboxylate is dehydrogenated by fuming nitric acid to diethyl azodicarboxylate in 70-80% yield. ... 

Preparative Method although widely available, diethyl azodi-carboxylate can be readily prepared from ethyl chloroformate and hydrazine, followed by oxidation of the resulting diethyl hydrazodicarboxylate. ... 

Both saturated and benzylic alcohols are dehydrogenated by refluxing with diethyl azodicarboxylate in benzene for 10 h. The azodicarboxylate is converted into hydrazodicarboxylate, while the alcohols give ketones in 51-87% yields [977. ... 

Diethyl and di-ter/-butyl hydrazodicarboxylate are dehydrogenated to diethyl- and di-tert-butylazodicarboxylate, respectively, by nitric acid [1184] and by iV-bromosuccinimide [1185] (equation 493). 

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