Diazoalkane 1,3-dipolar cycloaddition
The Diazoalkane 1,3-dipolar cycloaddition is a 1,3-dipolar cycloaddition (an organic reaction) between a 1,3-dipole diazo compound (notably diazomethane) and a dipolarophile. When the dipolarphile is an alkene, the reaction product is a pyrazoline.
The reaction product of a cycloaddition between diazomethane and trans-diethyl glutaconate is a 1-pyrazoline. This reaction is 100% regioselective because the diazo terminal nitrogen atom bonds exclusively to the alpha-carbon of the ester. The reaction is also a syn addition, and the configuration in the dipolarophile is preserved. The 1-pyrazoline is unstable and isomerizes to the 2-pyrazoline due to favorable conjugation with the ester group.
Another example of a diazo cycloaddition is a diazo-thioketone coupling.