Diphenyl Phosphorazidate (DPPA) − More Than Three Decades Later

More than thirty years have already elapsed since we introduced diphenyl phosphorazidate (diphenylphosphoryl azide, DPPA, (PhO)2P(O)N3) as a reagent for organic synthesis in 1972 (Figure 1). During these years, DPPA has been found to be effective for a variety of organic reactions as a versatile synthetic reagent. It is not too much to say that DPPA has secured an established position as a reagent. SciFinder will indicate you about 1,000 references about DPPA, and there will be found about 46,000 examples of reactions when you will search for DPPA as “ReactionReactant”. DPPA is now estimated to be produced over 50 tons per year in Japan and easily available commercially. my interests were aroused about reactivity of acyl phosphates which are a mixed anhydride from carboxylic and phosphoric acids. I synthesized the acyl phosphate 3 from benzoic acid (1) and diethyl phosphorochloridate (2) by a known procedure and the reaction of 3 was investigated. As one of several trials, the reaction with sodium azide was found to give benzoyl azide (4), as shown in Scheme 1. Although this reaction proceeded in two steps from benzoic acid (1), I thought that the acyl phosphate 6 would be temporally formed if the phosphorazidate 5 were used in place of the phosphorochloridate 2, and the acyl phosphate 6 would react in situ with the azide ion giving the acyl azide 7.