Cesium carbonate (Cs 2CO 3)

Abstract

(A) Fu and co-workers have used Cs 2CO 3 as the base in Suzuki cross-coupling reactions with yields up to 86%. When the same reactions were performed with Na 2CO 3 or NEt 3, the yields were 29% and 50%, respectively. (B) Littke and Fu have also shown the superiority of Cs 2CO 3 as compared with other bases in the Heck coupling of methylacrylate with chlorobenzene. K 2CO 3, NaOAc, NEt 3, K 3PO 4 and Cs 2CO 3 were used to provide yields of only 9%, 21%, 37%, 50% and 56%, respectively. (C) In the alkylation of phenols, Parrish and coworkers have shown the utility of Cs 2CO 3. Its use makes the alkylation possible even with highly reactive halides which, under other conditions, are prone to eliminations or other side reactions. (D) In natural product chemistry, Fujivara et al. have used Cs 2CO 3 in the key ring-forming step in the synthesis of lipogrammistin-A, originally isolated from the skin mucus of the grammistid fish. (E) Salvatore et al. used Cs 2CO 3 when constructing carbonates (not shown) and carbamates in good yield on solid support under CO 2 atmosphere and with TBAI as a co-catalyst. (F) Walla and Kappe have shown the utility of Cs 2CO 3 as a base when connecting benzoic acids to Merrifield resins under microwave irradiation. (G) Large macrocycles can be prepared using Cs 2CO 3. The reagent serves both as a base and as a cation template in the macrocyclization of dicarboxylic acids and dihalides to generate the desired crown ethers.