Cerium(IV) ammonium nitrate: A versatile oxidant in synthetic organic chemistry

Abstract

(A) CAN is used as a catalyst for the Michael addition of indole to α,β-unsaturated ketones under ultrasonic irradiation in excellent yields. Substitution takes place at the 3-position, and N-alkylation products are not observed. (B) CAN is used as a catalyst for selective esterification of N-Boc protected amino acids. The aliphatic/aromatic amino acids are selectively esterified without affecting the N-Boc protection. (C) A mild and efficient method has been developed for the chemoselective synthesis of geminal diacetates from aldehydes using acetic anhydride in the presence of a catalytic amount of CAN and ketones are unaffected. Also the deprotection of acylals is carried out by using water and CAN. (D) CAN is utilized in a novel synthesis of 2-arylbenzothiazoles by cyclization of the intermediate radical formed after initial oxidative coupling between thiophenols and aromatic nitriles in excellent yield. Also it was used in a one-pot synthesis of isooxazole derivatives from alkynes. (E) Yadav et al. reported a facile three-component condensation of aldehyde, β-keto ester and urea for the synthesis of 3,4-dihydro-pyrimidin-2(1H)-one in good yield mediated by CAN in a one-pot reaction. (F) An efficient mononitration of aromatic substrates was developed, using CAN suspended in dichloromethane in the presence of two equivalents of sulfuric acid. (G) Acetals and ketals are selectively deprotected in good to excellent yields under neutral or mildly basic conditions with a catalytic amount of CAN. The reaction tolerates a range of functional groups including unprotected secondary and tertiary alcohols, ketones, enones and triisopropyl ethers. Also, the aldehyde formed by deprotection is stable under the experimental conditions. (H) In an environmentally benign protocol, oxidative coupling of N,N-dialkylarylamines takes place in high yield using CAN as an oxidant in aqueous medium. (I) In a simple and mechanistically interesting reaction for CH oxidation culminating in Ritter amidation, Nair et al. reported a one-pot synthesis of acetamides from unactivated hydrocarbons using CAN in combination with sodium azide in acetonitrile medium. © Georg Thieme Verlag Stuttgart.