Figure 2.

Preparation of diazo compounds by (i) diazo transfer,^58,59 (ii) diazotization,^60,61 (iii) hydrazone decomposition^62,63 or hydrazone oxidation,^64,65 (iv) rearrangement of N-alkyl N-nitroso compounds,^8,66 (v) 1,3-disubstituted acyl or aryl triazine fragmentation,^67,68 and (vi) elaboration of other diazo compounds. Diazo compounds can be accessed from azides via acyl triazenes in a process mediated by a phosphinoester.^78,79