• Regioselective synthesis of 3-substituted indoles has been described using a sequence of N-silylation, 3-bromination of the 1-TBDMS detivative with NBS, 3-lithiation, treatment with an electrophile to introduce the 3-substituent, and desilylation with TBAF. Good overall yields are obtained for a range of electrophiles: J. Org. Chem., 59, 10 (1994); Org. Synth. Coll., 9, 417 (1998).
• Treatment with EtMgI followed by ZnCl2 leads to an N-zinc derivative. This undergoes acylation at the 3-position: Tetrahedron, 46, 6061 (1990).
• Lithiation of N-protected indoles usually occurs at the 2-position, e.g. benzenesulfonation of the 1-lithio derivative, 2-lithiation with LDA and treatment with pyridine-3,4-dicarboxylic anhydride. This sequence has been reported in a synthetic route to ellipticene and olivacine: J. Org. Chem., 57, 5891 (1992).
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Halogenation in the 2-position has been effected via the Li 1-carbamate and subsequent 2-lithiation: J. Org. Chem., 57, 2495 (1992):
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Treatment of the carbamate with Tri-n-butyltin chloride, A10746, followed by Stille coupling enables synthesis of 2-aryl- and 2-vinylindoles: J. Org. Chem., 60, 6218 (1995).
Harmful (Xn)
Nature polluting (N)
