Silver-catalyzed acylative annulation of N-propargylated indoles with α-keto acids: access to acylated pyrrolo[1,2-a]indoles

Abstract

This study describes the first carbon centered radical cyclization of N-propargyl indoles involving decarboxylation of α-keto acids in the presence of an Ag-catalyst. The present cascade carbon–carbon bond formation reactions provide C-acylated pyrrolo[1,2-a]indoles in good yields (25 examples). The amount of oxidant has a profound effect on the reaction to convert either the di-acylated products using 8 equiv. of K₂S₂O₈ or mono-acylated products using 2 equiv. of K₂S₂O₈. N-Propargyl pyrroles are also found to be suitable for delivering the corresponding 3H-pyrrolizines.