A process for the preparation of compounds of formula (I): wherein the general symbols are as defined in claim 1, which comprises reacting a compound of formula (V): wherein R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, R
8
, R
9
and R
18
are as defined in claim 1, and R
18
is especially nitro, chlorine or bromine, with an azide compound of formula (IX): wherein M and n are as defined in claim 1, especially with sodium azide.