Regioselective Direct C-Alkenylation of Indoles

5 years ago

Regioselective Direct C-Alkenylation of Indoles

Marino Petrini

The direct introduction of alkenyl groups into the indole framework avoiding its preliminary functionalization can be carried out using different synthetic strategies. Transition-metal complexes facilitate the C−H activation of indoles or alkenes allowing an efficient Csp2- Csp2 bond formation. The hydroindolation of alkynes catalyzed by the same metal complexes or various acidic promoters can also be pursued for the alkenylation process. Conjugate addition of electron-poor alkenes and direct condensation of carbonyl derivatives with indoles are also of interest for this purpose. The regiochemical control can be exploited using the intrinsic C-3 reactivity of the indole ring. The introduction of a suitable directing group at the nitrogen atom allows the preparation of C-2 alkenylated derivatives by transition metal catalyzed reactions. This review collects the fundamental contributions in this field reported in literature during the last fifteen years. Regioselectivity à la carte: The alkenylation of indoles can be efficiently addressed by a suitable choice of the substituent at the nitrogen atom. Hydrogen and simple alkyl groups drive the alkenylation at C-3. Conversely, acyl groups and nitrogen-containing heteroaromatic substituents favor the C-2 alkenylated derivatives in metal-catalyzed reactions. The nature of the metal complex employed also plays a crucial role in the regioselectivity.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201702124