Silver-Catalyzed C(sp²)–H Functionalization/C–O Cyclization Reaction at Room Temperature

Abstract

Silver-catalyzed C(sp(2))-H functionalization/C-O cyclization has been developed. The scalable reaction proceeds at room temperature in an open flask. The present method exhibits good functional-group compatibility because of the mild reaction conditions. Using a AgNO3 catalyst and a (NH4)2S2O8 oxidant in CH2Cl2/H2O solvent, various lactones are obtained in good to excellent yields. A kinetic isotope effect (KIE) study indicates that the reaction may occur via a radical process.

Electrochemical C−O Bond Formation: Facile Access to Aromatic Lactones

“…Pleasingly, the desired C−O cyclization products of thiophene ( 2 u – y , 2 aa ), indole ( 2 z ), and dibenzofuran ( 2 ac ) derivatives were achieved under constant‐current electrolysis. It is particularly noteworthy that this protocol tolerates pyridine‐containing substrates ( 2 ab and 2 ad ), which were not effectively transformed under previous reported radical C−O cyclization conditions …”

“…Among these synthetic protocols, radical C−H functionalization/C−O cyclization of 2‐arylbenzoic acids emerged as attractive and efficient methods, providing powerful tool for the preparation of such molecules (Scheme A). These processes are generally conducted using transition‐metal catalysts including Cu, Ag, aryl iodide, and photocatalysts in the presence of peroxides or persulfates as oxidants. However, a common feature of these methods is the requirement of stoichiometric chemical oxidants [e.g., (PhCO 2 ) 2 , AcOOH, PhCO 2 O t Bu, K 2 S 2 O 8 , (NH 4 ) 2 S 2 O 8 ] that led to waste generation.…”

Photocatalytic Dehydrogenative Lactonization of 2-Arylbenzoic Acids

“…It is worth mentioning that the regioselectivity obtained for benzocoumarin 2i under our conditions (92:8) is higher than the one reported for this compound using a copper catalyst at 75-85 ºC 9 and similar to the one obtained with a silver catalyst at room temperature. 11 Unfortunately, 2-(3`-pyridinyl)benzoic acid (1t) did not react under the established reaction conditions. Other heterocyclic substrates have not been systematically examined yet.…”

“…Very recently, a silver-catalyzed procedure has been reported for this transformation at room temperature, most likely via SET oxidation-radical cyclization. 11 Also very recently, the first organocatalyzed procedure that enables this transformation at room temperature was developed, avoiding the use of toxic and expensive transition metal catalysts (Scheme 1, path B). 12 In this context, we describe herein the first organocatalyzed dehydrogenative lactonization of 2-arylbenzoic acids promoted by visible-light.…”

Synthesis of DNA‐Intercalating 6H‐Benzo[c]chromen‐6‐one Derivatives through a Strategic Combination of Garratt–Braverman and Minisci Acyloxylation Reactions

“…for 15 h resulted in a much cleaner product profile in which the desired benzochromenone was obtained as the exclusive product in excellent yield and establishes the chemoselectivity of the reagent system chosen. The use of a larger amount of AgNO 3 (50 mol‐%) relative to reported quantities11a (20 mol‐%) sped up the aryl C–H activation thereby reducing the reaction time and suppressing the formation of side products, which result from over oxidation to lactols and lactones. By using the above‐mentioned synthetic protocol, seven new benzochromenone derivatives 5a–5g were synthesized (Table 2).…”