A compound of the general formula (2d) may be synthesized according to the following reaction formula: ##STR11## wherein R1, R2, R3, R4 and R are as defined above, R' is a lower alkyl group, and B is an unsubstituted or substituted alkylene chain of 2 to 6 carbon atoms (one methylene group in the alkylene chain may be replaced by an oxygen atom, a sulfur atom or a nitrogen atom, provided that the