Regiodivergent Synthesis of Pyrazolines with a Quaternary Carbon Center via Cycloaddition of Diazoesters to N-Purine-Substituted Allenes.

Diversity-oriented synthesis of pyrazoline derivatives that contain a quaternary carbon center has been achieved via the 1,3-dipolar cycloaddition between N-purine-substituted allenes and α-alkyl/aryl diazoesters. Using Pd ₂ (dba) ₃ as a catalyst, only 1-pyrazoline derivatives are produced in a regioselective manner. When DPPB is used as a catalyst, diverse 1-pyrazolines and 2-pyrazolines are obtained in moderate to good total yields.