| Abstract: | Diaminocyclopropenylium salts 14a,b react specifically with the phosphorylated diazomethanes 15a-e in dichloromethane in the presence of ethyl diisopropylamine and 1,5-diazabicyclo4.3.0]non-5-ene respectively to the 4,5-diaminopyridazines 16a-f. In contrast to that the 3,4-diaminopyridazines 17a-i are formed in the reaction of the salt 14c with the diazomethyl compounds 15a,c,d such as f-k in dichloromethane in the presence of the bicyclic base. With regard to the reaction mechanism the formation of the intermediate diazomethyl cyclopropenes ( 14a,b + 15 → 18 or 14c + 15 → 19 ) has to be interpreted in the sense of an electrophilic diazoalkane substitution reaction; neither 18 nor 19 can be isolated but undergo a fast 1,5]-cyclization to the betaines 20 or 21 , which finally isomerize to the pyridazines 16 or 17 by opening of the bridge bond. |
