Newsletter Issue 05 Sep-Oct 2008

Direct Acylation of Aryl Bromides with Aldehydes by Palladium Catalysis

The importance of arylketones does not need to be stressed. These compounds are common starting materials for very different compounds, and synthetic methods for them are always welcome. The classic method is of course the old Friedel-Crafts acylation, but coupling methods have been around for some years, though unfortunately they are sometimes troublesome and involve toxic metals. In the second issue of our newsletter previous number we selected a paper reporting conditions for the synthesis of aryl ketones from boronic acids and enol ethers. The method reported by the research group of Xiao (Liverpool, UK) uses aryl bromides as starting materials, but more interestingly, the source of the carbonyl compound is an aldehyde. The usual conditions involve reaction of an aryl bromide with the aldehyde using Pd(dba)2, dppp, pyrrolidine and molecular sieves in DMF at 115 °C for 6 h. Examples include coupling of aliphatic, benzylic and homobenzylic aldehydes with aryl bromides. The yields are usually excellent. The only heteroaryl bromide reported (2-bromothiophene) gives a modest 58% yield. Once again it is a great step forward since the days of Thallium to prepare alkyl aryl ketones.

J. Am. Chem. Soc., 130 (32), 10510–10511, 2008. See: 10.1021/ja804351z

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