Regioselective Direct C-Alkenylation of Indoles

The direct introduction of alkenyl groups into theindole 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 electronpoor 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.