the present invention comprises a method of synthesizing compounds of formula : wherein z , r 1 , r 2 , r 3 , r 4 and r 8 are as described herein ; comprising the steps of . reacting a compound of the formula ## str1 ## with an effective amount of ethyl cyanoacetate to form a compound of the formula ## str2 ## subjecting said compound to successive steps of nitrosating with a nitrosating agent to form a nitro group , reduction of the nitro group to an amine group with a reducing agent , and acylation of the amine group to an amide group with an acylating agent , to form compound ## str3 ## reacting said compound with an effective amount of a base to form compound ## str4 ## reacting said compound with an effective amount of a desulfurization compound to form compound ## str5 ## and subjecting said oxo group of compound to the successive steps of halogenation with a halogenating agent and displacement with an amine of the formula nr 1 r 2 , wherein r 1 and r 2 are as defined above , to form said compound of formula 1 .