Reactions of A-metallated indoles

A-Alkylation of indoles can utilise indol-l-ylsodiums, generated quantitatively as above, or it can involve a small concentration of an indolyl anion, produced by phase-transfer methods indole A-acylation and -arylsulfonyla-tion can also be achieved efficiently using phase-transfer methodology (see also section 17.1.4). 

Indolyl A-Grignards or, even better, their zinc equivalents undergo reaction predominantly at C-3 with a variety of carbon electrophiles such as aldehydes, ketones and acid halides, and even 2-bromothiazole.  

1-Lithioindoles are equally useful again, the position of attack depends on both solvent and the nature of the electrophile, as illustrated below.  

It is important to note that when an iV-metallated 3-substituted indole alkylates at carbon, necessarily a 3,3-disubstituted-3//-indole (an indolenine) is formed, which cannot rearomatise to form an indole (see section 17. L6 for rearrangements of 3,3-disubstituted indolenines). 

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