A coupling partner-dependent unsymmetrical C–H bond functionalization of N-phenoxyacetamides leading to the formation of sophisticated spirocyclic scaffolds is presented herein. To be specific, spiropyrazolonyl indazoles were formed from N-phenoxyacetamides and diazopyrazolones through sequential C–H bond cleavage and carbene insertion into two different phenyl moieties. On the other hand, bispirooxindoyl dihydrobenzofurans were formed from N-phenoxyacetamides and diazooxindoles through C–H bond cleavage and cascade carbene insertion into phenyl and oxindoyl moieties, respectively. These transformations not only provided effective strategies for the synthesis of the otherwise difficult-to-obtain spiroheterocyclic skeletons from simple and readily available substrates in a straightforward and atom-economic manner, but also disclosed some unprecedented reaction modes of N-phenoxyacetamides with cyclic diazo compounds. Structural elaborations of the products obtained herein furnished some valuable heptacyclic architectures. Mechanistic experiments and DFT calculations were also carried out to unveil the reaction mechanisms, especially the origin of the excellent chemoselectivity and diastereoselectivity demonstrated in the formation of bispirooxindoyl dihydrobenzofuran products.