Heterocyclic Chemistry at a Glance

Indoles 91

3-Lithio-indoles are usually generated via metal-halogen exchange processes, however direct 3-lithiation of indoles
with bulky N-trialkylsilyl substituents can also be used.

Metal–halogen exchange reactions for the preparation of indol-3-yl-lithiums necessarily require the absence of the
acidicN-hydrogen. Very-low temperatures must be maintained to prevent isomerisation to the more stable 2-lithiated
indole (an N-t-butyldimethylsilyl 3-lithio derivative is regiostable, even at 0 °C).

Palladium(0)-catalysed reactions

Extensive use of transition metal-catalysed cross-coupling chemistry has been made in the manipulation of indoles.
Boronic acids, stannanes and halides can all be utilised, as can trifl ates formed from 2- or 3-oxygenated indoles. Some
typical examples are shown below.