THE ASTOUNDING REACTION OF DIAZOMETHANE WITH DIMETHYL 2,3-DICYANOFUMARATE
The title reaction afforded the pyrazole derivatives 3 and 4 as well as the N-methyl-1,2,3-triazolecarboxylic esters 5 - 7.The poly-step sequence was clarified; the key intermediates are the 1-pyrazoline 18, the 2-pyrazoline 2, the 4H-pyrazole 12, the pyrazole 22, and methyl cyanoformate.
1,3-Dipolar Cycloadditions, 93. - The Astounding Reaction of Dimethyl 2,3-Dicyanofumarate with Diazomethane
The reaction with excess of diazomethane furnished methyl 4-cyano-1-methylpyrazole-5- and -3-carboxylate (2 and 3) as well as the three N-methyl-1,2,3-triazolecarboxylic esters 4-6.A mechanistic study revealed a poly-step sequence.The initial formation of the pyrazoline 8 proceeded normal.Base catalysis effected an equilibration of trans- and cis-2-pyrazoline, 8(*)12, followed by a fragmentation into methyl 4-cyano-3-pyrazolecarboxylate (26) and methyl cyanoformate (32); a 4H-pyrazole is supposed to be the key intermediate.The final products mentioned above emerged from further reaction of 26 and 32 with diazomethane.