Alternative Reactions to Friedel-crafts Acylation on Highly Activated Substrates

Friedel-Crafts acylation (FCAcyl) is the most widespread method used to prepare aryl ketones and aldehydes. However, depending on the type of group attached to the benzene, their derivatives influence the electronic characteristics and structural orientations of the compounds during acylation; thus, the groups are very important for the success of the reaction. The existence of strong electron-donating groups, such as polyhydroxy/ polyalkoxyphenols and anilines on the aromatic ring, makes this reaction difficult. To overcome these problems and with the aim of obtaining aromatic ketones from benzene compounds, appropriate methodologies were described. Therefore, this review consists of showing the importance and applicability of the Houben- Hoesch and Sugasawa reactions as alternatives for the Friedel-Crafts acylation of polyhydroxy/ polyalkoxyphenols and anilines, respectively. The main advances used in the original methodologies were also described. The use of these reactions as an alternative to the renowned Friedel-Crafts acylation reactions should be taken into consideration as an important synthetic tool because there is the possibility of reducing steps, with consequent improvement of yield, in addition to optimizing reaction performance.