Stilbene derivatives

A process for preparation of a stilbene represented by the formula (I):

• ##STR11## wherein R.sub.1 and R.sub.2 each independently represents hydrogen, lower alkyl or cycloalkyl, with the proviso that both R.sub.1 and R.sub.2 cannot be hydrogen simultaneously, R.sub.3 and R.sub.4 independently represent hydrogen, methyl, or trifluoromethyl, and R.sub.5 represents hydroxyl, lower alkoxyl, or lower alkylamino of the formula --NR.sub.6 R.sub.7, wherein R.sub.6 and R.sub.7 each independently represents hydrogen or lower alkyl, which comprises reacting a compound represented by the formula (II) ##STR12## wherein R.sub.1, R.sub.2 and R.sub.3 have the meanings previously assigned, with a compound represented by the formula (III) ##STR13## wherein R.sub.5 has the meaning previously assigned and X represents a group represented by the formula:
• ##STR14## wherein R.sub.4 has the meaning previously assigned and Y is an anion of an organic or inorganic acid or a dialkoxyphosphonylalkyl group represented by the formula:
• ##STR15## wherein R.sub.4 has the value previously assigned and R represents a lower alkyl group and, if desired, converting the carboxylic acid ester group represented by the formula --COR.sub.5 into the carboxylic acid group or a carbamide group.