Gold-Catalyzed Friedel-Crafts-Type Reactions

Gold-Catalyzed Friedel-Crafts-Type Reactions... 

The gold-catalyzed reaction of alkynes with aromatic units has been extensively studied [105-107]. This reaction allows the synthesis of polycyclic aromatic and heteroaromatic systems via Friedel-Crafts-type processes. Although, the C-H activation of aryl compounds by gold(lll) has been known for more than 70 years, it is accepted that the Friedel-Crafts-type reaction proceeds via [Au(alkyne)] complexes and subsequent electrophilic aromatic substitution with the arenes or heteroarene compounds. 

During the same year, both an acid-catalyzed [60] and a TiCl4-catalyzed [61] ortho-alkylation of anilines with styrene were published, but offering only a very low selectivity. The reaction of anisole and styrene catalyzed by Mo(CO)6 [62] afforded the corresponding branched diaryl product with a comparable yield and selectivity as shown by our protocol. Furthermore, Michelet and coworkers successfully employed substituted styrenes in a gold-catalyzed tandem Friedel-Crafts-type addition-carbocyclization reaction [63]. 

Scheme 1. Gold-catalyzed C—C-coupling reaction Friedel-Crafts-type or Michael-type reaction ...

The putative metal cationic intermediates can be interconnected into a series of cationic processes such as Friedel-Crafts, pinacol, Nazarov, Prins-type reactions. In Scheme 7.28, the gold-catalyzed cycloisomerization of 1,6-enynes is followed by an intramolecular nucleophilic attack by the proximate carbonyl to generate the tetrahydro-pyranyl cation, which participate in a Prins-type reaction to produce tricyclic compounds resembling the core structures of several terpenoids [52]. 

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