Experimental and Theoretical Studies on the Synthesis, Spectroscopic Data, and Reactions of Formyl Azide

摘要

Acyl azides 3 b and their Curtius rearrangement to produce isocyanates 4 b have been well-known for more than hundred years (Scheme 1). These azides are also of great importance in modern organic synthesis. The parent compound 3 a was investigated in about a dozen theoretically studies dealing with its structure, spectroscopic data, and various reactions. To the best of our knowledge, however, spectroscopic proof or any other indication for the existence of formyl azide (3 a) is still missing. There may be two reasons why 3 a has not been generated experimentally. Quantum chemical calculations predicted activation energies for the process 3a→4a that were significantly lower than those of the Curtius rearrangement reactions of acetyl or benzoyl azide (differences of 3.4-4.9 and 6.5-10.5 kcal mol~(-1), respectively). Thus, 3a should be highly unstable at ambient or even lower temperature. Furthermore, formyl chloride cannot be utilized as a convenient precursor of 3 a because this acyl chloride is a short-lived species, which excludes its simple synthesis and ease of handling.