| abstract |
The invention pertains to a process for preparing a compound of formula (1), wherein R 1 is independently chosen from C 1 -C 6 alkyl, cycloalkyl, aralkyl and aryl, and R 2 , R 3 and R 4 are independently chosen from hydrogen and C 1 -C 6 alkyl, cycloalkyl, aralkyl and aryl; which process comprises the steps of: a) contacting a compound of formula (2), wherein R 1 and R 2 are as above and M + is a monovalent metal ion, with a compound of formula (3), wherein R 3 and R 4 are as above, to form a compound of formula (4); and b) followed by contacting the compound of formula (4) with an acid to give a compound of formula (1), wherein step (a) and/or step (b) are conducted in continuous mode. |