Functionalization of indole at C-5 or C-7 via palladium-catalysed double carbonylation. A facile synthesis of indole ketocarboxamides and carboxamide dimers

Palladium-catalysed aminocarbonylation of 7-iodoindole derivatives (the parent compound and 5-bromo-7-iodoindole), as well as 5-iodoindole with various primary and secondary amines, including amino acid esters and chiral diamines, was carried out. In this way, a highly selective double carbonylation reaction at the C-7 was performed resulting in the formation of the corresponding indol-7-ylglyoxylamides when monoamines were used. The bromoarene moiety remained intact, so bromo-substituted glyoxylamides of practical importance have been synthesised in moderate to high yields. The use of chiral alkyl and aryl diamines as nucheophiles allowed the synthesis of a new family of dimeric 7-indole derivatives under moderate reaction conditions (10 bar, 100 °C). The aminocarbonylation at the C-5 position led to much lower chemoselectivities toward indol-5-ylglyoxylamides under similar conditions (40 bar CO, 50 °C).The aminocarbonylation of iodoindoles shows a strikingly different chemoselectivity depending on the basicity of the amine while primary and secondary amines of high basicity gave 2-ketocarboxamides in up to 98% chemoselectivity, aniline resulted in almost exclusive formation of the corresponding carboxamide product.