Functionalization of Indole at C-5 or C-7 via Palladium-Catalysed Double Carbonylation. A Facile Synthesis of Indole Ketocarboxamides and Carboxamide Dimers.

Takács, Attila and Marosvölgyi-Haskó, Diána and Kabak-Solt, Zsuzsanna and Damas, Liliana and Rodriguez, Fábio M.S. and Carrilho, Rui M. B. and Pineiro, Marta and Pereira, Mariette M. and Kollár, László (2016) Functionalization of Indole at C-5 or C-7 via Palladium-Catalysed Double Carbonylation. A Facile Synthesis of Indole Ketocarboxamides and Carboxamide Dimers. TETRAHEDRON, 72 (2). pp. 247-256. ISSN 0040-4020

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Abstract

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 ºC). The aminocarbonylation at the C-5 position led to much lower chemoselectivities toward indol-5-ylglyoxylamides under similar conditions (40 bar CO, 50 ºC). 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.

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