Microwave Chemistry Highlights
Cobalt Carbonyl-Mediated Synthesis of Ureas
Mats Larhed and co-workers from Uppsala University (Tetrahedron Lett. 2005, 46, 3335. DOI: 10.1016/j.tetlet.2005.03.076) have reported on a novel and very fast gas-free carbonylation method for the preparation of ureas starting from primary amines. Under high intensity microwave heating with an in situ generation of intermediate isocyanates from Co2(CO)8, amines have been converted to the corresponding ureas within 10 s of reaction times. This method has facilitated the preparation of symmetrical and unsymmetrical ureas in good to moderate yields respectively.
One Step Synthesis of 3,5-Disubstituted 1,2,4-Triazoles
A recent publication by Kap-Sun Yeung and co-workers from Bristol-Myers Squibb (Tetrahedron Lett. 2005, 46, 3429. DOI: 10.1016/j.tetlet.2005.02.167) describes a convenient and efficient one step, base-catalyzed synthesis of 3,5-disubstituted 1,2,4-triazoles by the condensation of a nitrile and a hydrazide. Under the reaction conditions, a diverse range of functionality and heterocycles are tolerated. The reactivity of the nitrile partner is relatively insensitive to electronic effects.
Multistep Synthesis of Functionalized 4-Arylquinolin-2(1H)-ones
An efficient multistep synthesis of biologically active 4-aryl-3-alkenyl-substituted quinolin-2-(1H)-ones has been demonstrated by our group (J. Org. Chem. 2005, 70, 3864, DOI: 10.1021/jo0502549). All the synthetic transformations (six steps) required for the synthesis of the desired target quinolin-2-(1H)-ones have been carried out under controlled microwave heating. The key steps in the synthesis include a sequential Pd catalyzed Suzuki/Heck scaffold decoration method to allow introduction of substituents late in the synthetic scheme and facilitate preparation of 2(1H)-quinolinone analogues with a greater diversity for potentially generating combinatorial libraries.
Preparation of 2-Aminosulfonamide-1,3,4-oxadiazoles using Polymer-Supported Reagents and Microwave Heating
Steven Ley and co-workers from the University of Cambridge (Tetrahedron 2005, 61, 5323. DOI: 10.1016/j.tet.2005.03.062) have reported on a symbiotic combination of solid-supported reagents and microwave-assisted organic synthesis to rapidly generate compound libraries of 5-substituted-2-amino-1,3,4-oxadiazoles and their corresponding thiadiazole analogues. A one-pot preparation of the 2-aminosulfonylated analogues through a three component coupling of an acylhydrazine, an isocyanate and sulfonyl chloride promoted by a polymer-supported phosphazine base (PS-BEMP) under microwave heating is also described.