Biomimetic Mn(III) porphyrin-catalyzed aromaticity-breaking epoxidation of electron-deficient naphthalene

Abstract

Abstract Selective catalytic aromaticity-breaking epoxidation of arenes remains an ongoing research challenge, attributed to the stability of aromatic systems, the occurrence of over-oxidation, and the instability of epoxides. Epoxides, recognized as short-lived and highly reactive intermediates, are prone to undergo the “NIH-shift” rearrangement to yield the hydroxylated products. Herein, we report the synthesis and characterization of several electron-deficient naphthalene epoxides that disrupt the aromaticity of naphthalene. Their formation is highly dependent on the substrate, especially on the specific substitution pattern. This achievement is enabled by using mild biomimetic manganese porphyrins as catalysts and iodosylbenzene as an oxidant. The strategic employment of electron-withdrawing substitution on naphthalenes enables a chemoselective switch from hydroxylation to epoxidation. Experimental studies and theoretical calculations elucidate the possible underlying mechanisms of epoxidation and hydroxylation: epoxidation is likely mediated by a radical mechanism, whereas hydroxylation predominantly follows a zwitterionic pathway.