C–H Bond Functionalization of Benzoic Acid: Catalytic Synthesis of 2-Hydroxy-6H-benzo[c]chromen-6-ones Using (Cp*IrCl₂)₂

Abstract

Catalytic H/D exchange reactions of benzene and benzoic acid with deuterated solvents have been studied using (Cp*IrCl2)2. A 1:1 mixture of D2O/CD3OD produced the highest turnover numbers for benzene. High levels of deuterium incorporation into benzoic acid were observed only when sodium acetate was added to the reaction mixture. Attempts at producing hydroxybenzoic acid by catalytic C–H functionalization of benzoic acid with benzoquinone were unsuccessful. Instead, 2-hydroxy-6H-benzo[c]chromen-6-one was isolated as the major product. An array of substituted benzoic acids was analyzed for this functionalization reaction. Preliminary mechanistic studies indicate that the benzochromenones are formed by C–H bond activation of benzoic acid followed by insertion of benzoquinone into the iridium–carbon bond.

Iridium‐Catalyzed Direct CH Amidation with Weakly Coordinating Carbonyl Directing Groups under Mild Conditions

“…To examine the above hypothesis, we screened various reaction conditions for the amidation of ethyl benzoate (1 a) with an equimolar amount of para-toluenesulfonyl azide (2 a) that are based on our recently developed procedures for CÀH amidation [9,10] using a {Cp*Ir III } catalyst system (Table 1; Cp* = pentamethylcyclopentadienyl). [11] When a silver salt, which is required for the generation of a cationic iridium species, was used as the sole additive (entry 1), no reaction occurred. However, the use of certain additional additives was found to initiate the amidation to some extent.…”

A Rhodium‐Catalyzed Cascade Cyclization: Direct Synthesis of N‐Substituted Phthalimides from Isocyanates and Benzoic Acids

“…No desired product was detected in the presence of 5 mol% of [Cp*RhCl 2 ] 2 in toluene at 100 °C (Table 1, entry 1). Because sodium acetate promotes ortho CH bond activation of benzoic acids,16 we tested the effect of this salt on our reaction. We were pleased to find that the cyclization product was formed in 65% NMR yield in the presence of 2.0 equiv.…”

Carboxylic Acids as Directing Groups for C−H Bond Functionalization

“…Other electrophiles : In 2011, Ison and co‐workers reported a carboxylate‐directed C−H functionalization strategy for the synthesis of benzochromenone derivatives by [{IrCp*Cl 2 } 2 ]‐catalyzed coupling of benzoic acids and benzoquinones . Preliminary mechanistic studies support the idea that the benzochromenones are formed by C−H bond activation of benzoic acid followed by insertion of benzoquinone into the Ir−C bond.…”