One-Pot Synthesis of Spirocyclic or Fused Pyrazoles from Cyclic Ketones: Calcium Carbide as the Carbon Source in Ring Expansion.

N-Tosylhydrazones generated in situ from cyclic ketones smoothly underwent a [3 + 2] cycloaddition to afford saturated spirocyclic pyrazoles and further transformed to the fused analogues via a ring expansion in certain cases. An inexpensive and renewable resource, calcium carbide, was utilized as the carbon source in the ring expansion. The salient features of this reaction include widely available starting materials, convenient one-pot/two-step procedure, great efficiency, and high regioselectivity. Remarkably, this reaction underwent a [1,5]-sigmatropic rearrangement process, which was supported by deuterium-labeling experiments.