Base-mediated formal [3＋2] cycloaddition of β,γ-alkenyl esters and p-TsN3 for the synthesis of pyrazoles

A novel 1,8-diazabicyclo[5.4.0]undec-7-ene （DBU）-mediated formal cycloaddition of β,γ-alkenyl esters with p-tolylsulfonylazide （p-TsN3） for the synthesis of 3,5-disubstituted pyrazoles has been developed. The reaction proceeded through diazotization of β,γ-alkenyl esters sequential with thermodynamic cyclization, p-Tolylsulfonylazide played a role as a source of two-nitrogen synthons. The reaction employs readily available starting materials, tolerates a wide range of functional groups, and proceeds under mild conditions.