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.