Friedel microwave-assisted

In 2000, Dubac s group reported the microwave-assisted Friedel-Crafts acylation of slightly activated and deactivated arenes under solvent-free conditions with FeCl3 as catalyst. Here, for the acylation of toluene a 90% product yield is obtained after 5 min of irradiation and an overall reaction time of 30 min in the presence of only 5 mol% of FeCl3. A sequential MW irradiation at 300 W afforded the acylation of fluorobenzene with 2 -chlorobenzoyl chloride, with a surprisingly high yield of 92% of 2-chloro-4 -fluorobenzophenone (Scheme 6.11). 

The novice reader may think that the subject is an emerging field however, the green chemistry name is an umbrella for many well-established ideas and techniques that already exist in the literature. None of the techniques under the green technology label can therefore be considered new. For example, the first room-temperature ionic liquid, ethylammonium nitrate [EtNH3] [N03] , which melts at 12°C was discovered by Paul Walden in 1914 [40], Ionic liquids were also observed in Friedel-Crafts acylation and alkylation reactions [41,42], The reader is directed to two reviews that chronicle the historical development of ionic liquids [43,44]. Microwave-assisted synthesis was developed by Gedeye and Westaway at Laurentian University in Sudbury, Canada [45-48],... 

One further application of the microwave-assisted Wolff rearrangement of 2-diazo-1,3-dicarbonyl conpounds involves the direct Friedel-Crafts a-ketoacylation of heteroaromatic compounds in the absence of any catalyst or additive and under halogen-free conditions tScheme 3.26k In contrast to standard Friedel-Crafts reactions that are often conplicated by regioselectivity and/or efficiency issues, the microwave-assisted Friedel-Crafts a-ketoacylation via a-oxo-ketenes proceeded cleanly and with high regioselectivity. It should be noted at there are only a few known exanples of formation of carbon-carbon bonds by... 

A similar organocatalytic quadruple domino Friedel-Crafts/Michael/Michael/ aldol condensation reaction initiated by Friedel-Crafts reaction of indole to acrolein was also developed by Enders et al. [48], as well as a microwave-assisted qnadruple cascade organocatalytic Michael/Henry condensation/Michael/aldol condensation anploying acetaldehyde and nitroalkenes as substrates [49]. 

In 2004, Ricci and coworkers reported a sustainable Friedel-Crafts adulation of nitroalkenes with various aromatic and heteroaromatic substrates utilising 10 mol% of thiourea 8 under solvent-free reaction conditions. When applied to indoles, this method provides excellent yields and high selectivities (Scheme 19.8). Additionally, allqrlation at the difficult 2-position of the 3-methylindole was accomplished in a solvent-free reaction with the assistance of microwave irradiation (MW). 

---