Studies on heteroaromaticity. XV . the 1,3‐dipolar cycloaddition reaction of 5‐nitro‐2‐furyldiazomethane

The 1,3‐dipolar cycloaddition reaction of 5‐nitro‐2‐furyldiazomethane ( 1 ) with acrylonitrile, acrylamide, methyl acrylate, diethyl fumarate, methyl methacrylate and methyl cinnamate afforded the corresponding 3‐substituted pyrazolines. ( 2a‐f ). Similarly the pyrazoles ( 3b‐d ) were prepared by addition of 1 to acetylenic compounds such as diethyl acetylenedicarboxylate, methyl phenylpropiolate and cyanoacetylene. Reaction of 1 with fumaronitrile and ω‐nitro‐styrene gave also the corresponding pyrazoles ( 3a and 3e ) instead of the pyrazolines. 3‐(5′‐Nitro‐2′‐furyl)‐4‐phenyl‐5‐carbomethoxypyrazoline ( 2f ) was oxidized with lead tetraacetate to the corresponding pyrazole ( 3f ), which was different from 3c , an addition product of 1 with methyl phenylpropiolate. 3‐(5′‐Nitro‐2′‐furyl)‐5‐carbamidopyrazoline ( 2b ) was pyrolyzed to the corresponding cyclopropane derivative 4 in low yield.