Reactions with Nucleophilic Reagents See Also Section

3 Reactions with nucleophilic reagents (see also section 17.14.4) 

As with pyrroles and furans, indoles undergo very few nucleophilic substitution processes. Those that are known involve special situations benzene-ring-nitro-indoles, in which the iV-hydrogen has been removed as well, undergo vicarious nucleophilic substitutions (section 2.3.3).  

In chromium carbonyl complexes of indole, the metal is associated with the benzene ring, hence nucleophilic additions take place in that ring, usually at C-4 the example shows the relatively unusual attack at C-7 this regioselectivity can be induced to revert to the usual C-4 if an indole with a bulky A-protecting group is utilised.  

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