Synthesis and reactions of ethyl 3‐acetyl‐8‐cyano‐6,7‐dimethylpyrrolo[1,2‐ a ]pyrimidine‐4‐carboxylate and related compounds

The reactions of 3‐acetyl‐4‐ethoxycarbonyl‐ or 3,4‐diethoxycarbonylpyrrolo[1,2‐ a ]pyrimidine derivatives 7a,b , which were prepared by condensation of the 2‐aminopyrrole ( 4 ) with ethyl 3‐ethoxymethylene‐2,4‐dioxovalerate ( 5a ) or ethyl ethoxymethyleneoxaloacetate ( 5b ), with diazomethane are described. Thus, reaction of 7a , with diazomethane gave ethyl 2a‐acetyl‐7‐cyano‐2a,3a‐dihydro‐5,6‐dimethyl‐3 H ‐cyclopropa[e]pyrrolo[1,2‐ a ]pyrimidine‐3a‐carboxylate ( 11 ) in 74% yield, which was readily transformed into the 1‐pyrrol‐2‐yl‐pyrrole ( 18 ) by treatment with potassium hydroxide. On the other hand, reaction of 7b with diazomethane afforded three products whose structures were assigned as diethyl 7‐cyano‐2a,3a‐dihydro‐5,6‐dimethyl‐3H‐cyclopropa[e]pyrrolo[1,2‐ a ]pyrimidine‐2a,3a‐carboxylate ( 20 ), 6‐cyano‐7,8‐dimethyl‐3a,3b,5,9a‐tetrahydro‐4 H ‐aziridino[c]‐1 H or 3 H ‐pyrazolo[3,4‐e]pyrrolo[1,2‐a]pyrimidine‐3a,9a‐dicarboxylates ( 21,22 ). Ring Transformation of 20 to 25 was not observed.