Remote C−H Pyridylation of Hydroxamates through Direct Photoexcitation of O‐Aryl Oxime Pyridinium Intermediates

Abstract

AbstractHerein, we report an efficient strategy for the remote C−H pyridylation of hydroxamates with excellent ortho‐selectivity by designing a new class of photon‐absorbing O‐aryl oxime pyridinium salts generated in situ from the corresponding pyridines and hydroxamates. When irradiated by visible light, the photoexcitation of oxime pyridinium intermediates generates iminyl radicals via the photolytic N−O bond cleavage, which does not require an external photocatalyst. The efficiency of light absorption and N−O bond cleavage of the oxime pyridinium salts can be modulated through the electronic effect of substitution on the O‐aryl ring. The resultant iminyl radicals enable the installation of pyridyl rings at the γ‐CN position, which yields synthetically valuable C2‐substituted pyridyl derivatives. This novel synthetic approach provides significant advantages in terms of both efficiency and simplicity and exhibits broad functional group tolerance in complex settings under mild and metal‐free conditions.