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We know that phenol and aniline, despite being strongly activating, are unable to to undergo Friedel-Crafts reactions because they form complexes with $\ce{AlCl3}$, thanks to the lone pair on nitrogen and oxygen atoms.

However, according to my notes (and Google) anisole does undergo Friedel-Crafts reactions. How can it be possible, why is there no complex formation this time?

Also, I wanted to know how can we say that a certain group like $\ce{OH}$ will surely form a complex? Is containing a lone pair a sufficient condition?

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  • $\begingroup$ What complex does it form? $\endgroup$ – Yashas Apr 8 '17 at 2:59
  • $\begingroup$ @Yashas For eg, phenol forms Ar-(OH+)-(AlCl3-) $\endgroup$ – Sawarnik Apr 8 '17 at 4:20
  • $\begingroup$ Not sure if this correct, but you could use alkyl triflate, instead of alkyl chloride + $\ce{AlCl3}$. Triflate is a good leaving group and can generate carbocations with easily react with the activated ring of phenol or aniline. $\endgroup$ – Pritt says Reinstate Monica Apr 22 '17 at 4:27
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Friedel-Crafts acylation of anisole with acetyl chloride and aluminium chloride as catalyst is a standard laboratory procedure to synthesize acetanisole.

            source: Wikipedia, user Jü

The fact that this reaction is possible does not imply that there is no complex formation with $\ce{AlCl3}$. On the contrary, it is quite probable that such complexes do form due to the interaction of the methoxy oxygen with $\ce{AlCl3}$.

Therefore, and to compensate the formation of complexes with the resulting ketone, $\ce{AlCl3}$ is added in more than two-fold excess in the above synthesis.

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