in dichloromethane; pentane (inert atmosphere); -30°C, 1 h; under similar conditions a mixture (elem. anal.) of 5 tautomeric compounds (assignment by NMR) is obtained; removal of solvents (vac., -30°C), chromy. (SiO2; CH2Cl2/n-pentane gradient, -35°C), solvent removal (vac., -30°C), the twomain byproducts could not be obtained pure;