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Abstract Direct and regioselective functionalization of pyridine is a topic of high scientific and technological importance. In spite of extensive efforts, the regioselective functionalization of pyridine still remains a significant challenge due to their low reactivity and presence of Lewis‐basic sp²nitrogen. Here, we studied the effect of hydrogen bonding interactions on the regiochemical outcome of Pd‐mediated C−H activation of pyridine by utilizing DFT calculations. We demonstrated that hydrogen bonding can act as a second independent factor to override the inherent regioselectivity of pyridine. This novel approach complements previously reported strategies, such as: (a) coordination of pyridine to transition metal center via its N‐center, (b) installation of directing group (DG) and then coordination of pyridine to the transition metal center via this DG (i. e. chelation assistant strategy), (c) protection of its nitrogen lone pair with N‐oxide or N‐imino groups or with Lewis acids, (d) the inherent positional reactivity of C−H bonds based on the electronic or steric properties of the substituents, and (e) by the identity of the oxidant used. We have also demonstrated that the oxidation state of the Pd catalyst has impact on the regiochemical outcome of the C−H activation step in pyridine. The implications of our study for regioselective C−H functionalization catalyst design of heteroarenes are twofold: It demonstrates (1) hydrogen bonding as a viable design principle, and (2) Pd(IV) as a catalyst for C−H functionalization. 

Abstract Transition metal‐catalyzed C−H bond oxidation of free carboxylic acid stands as an economic, selective, and efficient strategy to generate lactones, hydroxylated products, and acetoxylated products and attracts much of the chemists’ attention. Herein, we performed a density functional theory study on the mechanism and selectivity in Pd‐catalyzed and MPAA ligand‐enabled C−H bond acetoxylation reaction. It was found that the ligand, base, and substrate are important in determining the reaction mechanism and the selectivity. The acetic anhydride additive is critical in leading the reaction to be acetoxylation, instead of the lactonization, through a facile σ‐bond metathesis mechanism that leads to the Pd‐OAc in‐termediate. Our study sheds light on the further development of transition metal‐catalyzed C−H bond oxidation reactions. 

Abstract Computational studies revealed that dirhodium tetrakis(1,2,2‐triarylcyclopropanecarboxylate) (Rh₂(TPCP)₄) catalysts adopt distinctive high symmetry orientations, which are dependent on the nature of the aryl substitution pattern. The parent catalyst, Rh₂(TPCP)₄, and those with ap‐substituent at the C1 aryl, such as Rh₂(p‐BrTPCP)₄and Rh₂(p‐PhTPCP)₄, adopt aC₂‐symmetric structure. Rh₂(3,5‐di(p‐^tBuC₆H₄)TPCP)₄, 3,5‐disubstituted at the C1 aryl, adopts aD₂‐symmetric structure, whereas catalysts with ano‐substituent at the C1 aryl, such as Rh₂(o‐Cl‐5‐BrTPCP)_4,adopt aC₄‐symmetric structure.