C(sp3)–H Oxidation of Spiroguanidine-Containing Cyclopentanes

A C(sp³)–H oxidation reaction for spiroguanidine compounds with 5-membered rings was developed. The introduction of a cyclopentane-fused aminomethylpyridine as a directing group to the amide linkage of the cyclic guanidine moiety, using H₂O₂–urea in trifluoroethanol, enabled oxidation at the spiro β-position of the cyclopentane ring. This allowed selective introduction of a hydroxy group at the spiro β-position and was applicable to cyclopentane compounds with various substituents, including those challenging to functionalize with common oxidation methods.