| 摘要 |
The invention relates to an improved method for producing compounds of formula (1) on an industrial scale. In formula (1), R<SUP>1</SUP>, R<SUP>2</SUP> and R<SUP>3</SUP> respectively independently represent C<SUB>1-6</SUB> alkyl, C<SUB>2-6</SUB> alkenyl, C<SUB>2-6</SUB> alkinyl or aryl, and R<SUP>4</SUP> represents H, OC<SUB>1-6</SUB> alkyl, Oaryl, OH, C<SUB>1-6</SUB> alkyl, halogen, CN or NO<SUB>2</SUB>. |
