Cr(III)-Salen-Catalyzed Enantioselective C3-Aryloxylation of Spiroepoxy Oxindoles

We report the first metal-salen-catalyzed switchable ortho-C- and O-alkylation of phenols with spiroepoxides at the tertiary sp³-carbon center of spiroepoxides. Catalyst choice between chiral Cr(III)-salen and chiral Co(III)-salen OTf enables a rare divergence in reactivity: the chiral salen Cr(III)Cl catalyst directs the reaction toward highly enantioselective C3-aryloxylation to afford 3-aryloxy-oxindole-3-methanols (up to 98% ee), whereas salenCo(III)OTf (cat. B) switches the outcome to the complementary C3-ortho-arylation pathway without stereoinduction. The method tolerates various N-protecting groups and aromatic substitution patterns, creating a diverse library of functionalized oxindoles. Mass spectrometric studies reveal catalyst-substrate complexes and (hetero)dimeric assemblies, providing insight into a mechanistic pathway that favors aryloxylation. The method also achieves the first asymmetric synthesis of spiro[benzo[b][1,4]dioxine-2,3'-indolin]-2'-one.