General and Selective C-3 Alkylation of Indoles with Primary Alcohols by a Reusable Pt Nanocluster Catalyst

摘要

The indole scaffold is one of most relevant structures found in natural products, pharmaceuticals ingredients, functional materials and agro-chemicals.[1] C-3 substituted indoles are of particular importance for the construction of various biologically active molecules.[2-3] Conventional methodologies for the generation of C-3 substituted indoles require stoichiometric amount of Lewis acids, which have serious drawbacks such as poor regioselectivity, formation of salt wastes and use of hazardous reagents.[4-6] Recently developed methods for the generation of C-3-alkylated indoles are based on Friedel-Crafts reactions in the presence of Lewis and Br?nsted acids or organocatalysts, which suffer from necessities of additives and limited substrate scopes.[7-11] C-3 alkylation of indoles using propargylic or aromatic alcohol[12-16] or benzylmethyl carbonate[17] have been recently developed as more environmentally benign methods, though they suffer from limited scope of alcohols. Very recently, Yus and co-workers showed non-catalytic C-3 alkylation by alcohol through a hydrogen-autotransfer strategy with a stoichiometric amount of base (130 mol% KOH). However this method only worked with activated (aromatic) alcohols.[18]