Synthesis of Pyrazolines via (3+2) Cycloaddition of Nitrile Imines and N-Silyl Enamines

The synthesis of tricyclic fused pyrazolines from N -silyl enamines and nitrile imines is presented. N -Silyl enamines are an emerging class of enamines that can be used as free enamine surrogates. The N -silyl enamines, prepared from readily available isoquinolines, underwent (3+2) cycloaddition with a wide range of nitrile imines to form the corresponding pyrazolines in moderate to good yields. This cascade protocol entailed the in situ utilization of both N -silyl enamine and nitrile imine intermediates.