abstract |
The invention relates to an improved method for producing compounds of formula (1) on an industrial scale. In formula (1), R1, R2 and R3 respectively independently represent C1-6 alkyl, C2-6 alkenyl, C2-6 alkinyl or aryl, and R4 represents H, OC1-6 alkyl, Oaryl, OH, C1-6 alkyl, halogen, CN or NO2. |