The reaction is carried out in a suitable inert solvent such as benzene, toluene, dimethylformamide or tetrahydrofuran, preferably in the presence of an acid scavenger (e.g. sodium hydride, sodium amide, sodium methoxide, sodium ethoxide, potassium hydroxide, sodium hydroxide) at -10??? C. to 150??? C. for 1 to 20 hours to give the compound of formula: ##STR24## wherein each symbol is as defined a