5-Bromoindole, halogen metal exchange

Halogen-metal exchange has also been used to produce 7-substituted indole derivatives, (Scheme 29) with the potassium salt of 7-bromoindole... 

As noted earlier (Scheme 4), 3-iodo-A -(phenylsulfonyl)indole 6 was lithiated selectively at C2 (thus avoiding halogen-metal exchange) by treatment with LDA [14, 183-185]. This selectivity has also been observed with 3-bromoindole 43 [159, 183, 184, 186], functionalized 3-bromoindoles (not shown) [159, 187], and 3-cyanoindole 44 [103, 188]. Examples of the C2-lithiation of these substrates in the synthesis of 2,3-disubstituted indoles 39 are shown below (Table 6). 

Amazingly, metal-halogen exchange can be achieved with each of the benzene ring-bromoindoles without iV-protection the indole is first converted into its N-potassio-salt. ... 

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