"The reaction of a compound of formula III wherein Ya is hydrogen and Xa is halogen, while Ra and Rb are as defined for compounds of formula III, with a salt of hydrazoic acid to form a compound of formula IV, as defined above, or of a compound of formula Va wherein Xa is halogen, especially iodine or especially chlorine or bromine, while Ra and Rb are as defined for compounds of formula III, with" . . . .