Revisiting 2-Alkoxy-3-bromoindolines: Control C-2 vs. C-3 Elimination for Regioselective Synthesis of Alkoxyindoles

抄録

The regioselective synthesis of both 2- and 3-alkoxyindoles from a common intermediate, 2-alkoxy-3-bromoindolines (ROBIN), is described. The 2-alkoxyindoles are obtained by a base-promoted regioselective elimination of HBr from ROBIN, whereas the synthesis of 3-alkoxyindoles is achieved by a silver-mediated alkoxylation followed by an acid-promoted elimination of alkoxide. This key elimination features the complete regioselectivity and no need for catalysts, that makes it have potential synthetic applications. Furthermore, this protocol is user friendly because ROBIN is able to be prepared from commercially available indoles and is a bench-stable easy-to-handle crystalline substrate, thus allowing the concise synthesis of a variety of both 2- and 3-alkoxyindoles.