PURPOSE: To obtain a 5-hydroxy-N-substituted indole derivative under mild conditions in simple treatment and good yield by reacting a phenol derivative having α,β-unsaturated cyclic double bond at m-position with a diazonium salt as starting materials.

CONSTITUTION: A phenol derivative expressed by formula I [R1, R5 and R6 are H, alkyl, halogen, alkenyl, alkoxy, aryl, acyl or aralkyl; H or a group capable of eliminating by diazo-coupling reaction may be attached at p-position to OH; Ra and Rb are mutually bonded to form a 4 to 12-membered ring consisting of nonmetallic atom (N, S and/O)] is subjected to coupling reaction with a diazonium salt expressed by formula II (R7 is diazonium salt residue; X is anion) in an inert solvent at low temperature to provide the aimed com pound expressed by formula III useful for various kinds of medicines or syn thetic intermediate for alkaloid, raw material for a series of antibiotics such as mytomycin.