Microwave irradiation, aryl ketones

In a related three-component reaction procedure, aryl methyl ketones 724 have been combined with aryl aldehydes 725 and urea 726 at room temperature, using trimethylsilyl iodide as catalyst, to give 4,6-diaryl-3,4-dihydro-2(177)-pyrimidinones 727 <2005HCA2996>. A procedure using zinc iodide and microwave irradiation gave similar products <2007T1981>. 

Varma, R.S., Kumar, D. and Liesen, P.J., Solid state synthesis of 2 arnvlbcnzn [ b ] fui.tns, thiazoles and 3-aryl-5,6-dihydroimidazo [2,1 fo] [ 1,3] thiazoles from a-tosyloxy ketones using microwave irradiation, /. Chem. Soc., Perkin Trans. 1, 1998,4093-4096. 

An intramolecular cychzation of an aryl ether to the carbonyl of a pendant aryl ketone, on clay with microwave irradiation, led to a benzofuran via Friedel-Crafts cyclization and ehmination of water. 

Amino-3-cyano-thiophenes or 2-amino-thiophene-3-esters result from this route, generally conducted as a one-pot process, involving a ketone that has an a-methylene, ethyl cyanoacetate or malononitrile, sulfur, and morpholine. Various improvements to the original procedure include using microwave irradiation on solid snpport, or with potassium fluoride on alumina as the base, or solvent-free,and using morpho-lininm acetate in excess morpholine for aryl alkyl ketones. 

Trabanco and coworkers developed an operationally simple method for the a-allylation of aryl alkanones with ally] alcohol under microwave irradiation conditions (Scheme 10.35) [77]. The corresponding a-allyl ketones were obtained in moderate to good yields with minor quantities of diallylation by-products. 

The use of microwave technology in synthesis continues to gain popularity. A microwave-enhanced synthesis of 3-aryl-4-hydroxyquinolin-2(l//)-oncs by cyclization of a malonodianilide under solvent free conditions was reported <01TL1367>. Microwave irradiation was also used to prepare quinolones from anthranilic acid and ketones <01SC3647>. A microwave promoted, intramolecular cyclization of an isocyanate in the ortho position of a stilbene derivative to afford a quinolone derivative was also reported <01T6197>. 

The Bredereck-type synthesis, which is well known as a conventional preparation of pyrimidine derivatives, generally requires a reaction temperature of more than 160 °C, and the product yield is moderate. A simple, high-yielding synthesis of pyrimidines from ketones in the presence of HMDS and formamide is reported. Under microwave irradiation, heteroaromatic, aryl, aliphatic, and cyclic ketones cyclized to give pyrimidines in good yields. 

The diketone 20 was synthesized from the aldol condensation of aryl methyl ketones 19 and benzil. The benzilic acid type rearrangement of 4-aryl-l,2-diphenyl-2-butene-l,4-diones (20) to 5-aryl-3,3-diphenyl-2,3-dihydro-l. -2-pyrrolones (21) has been accomplished under microwave irradiation using ammonium formate in PEG-200. ... 

Very recently, Jun et al. [179] have described the synthesis of isoquinoUnes 181 and pyridines 182 by the [Cp RhCy2-catalyzed Al-annulation reaction between aryl or a,p-unsaturated ketones 179-180, alkynes 178, and NH OAc, employing stoichiometric amounts of Cu(OAc)j as the oxidant and microwave irradiation. The reaction is successful with a wide family of arylketones 179 and enones 180 to afford the desired isoquinolines 181 and pyridines 182 in good to excellent yields (Scheme 3.69). A four-component reaction could be developed by in situ generation of enones by aldol reaction between an enolizable ketone and formaldehyde, affording the desired products in moderate yields. The proposed mechanism involves the Rh" -promoted consecutive N—H and p-C—H bond activation of imine XXXVII, generated from ketone/enone and NH, ... 

In 2003, an extremely fast protocol for the cobalt carbonyl mediated formation of symmetric diaryl ketones from aryl halides was disclosed by Larhed and coworkers [38]. Microwave irradiation of aryl iodides and Co2(CO)g in acetonitrile for 10 s or less was enough to produce high yields (57-97%) of symmetric diaryhnethanones (Scheme 4.25). Please note that the Co2(CO)8-mediated chemistry was performed without an additional transition metal catalyst. 

---