A simple two steps ytterbium triflate‐catalysed preparation of 2,2‐dimethyl‐2<i>h</i>‐chromenes from salicylaldehydes and 2‐methylpropene

Abstract

Abstract magnified image The preparation of various 2,2‐dimethyl‐2 H ‐chromenes was achieved in two steps via an ytterbium triflate‐catalysed reaction between salicylaldehydes, trimethylorthoformate and 2‐methylpropene. From salicylaldehyde, two reaction products were characterised: 4‐methoxy‐2,2‐dimethylchroman and 2‐(1,3‐dimethoxy‐3‐methylbutyl)phenol. The former compound probably results from a Lewis acid‐catalysed [2+4] cycloaddition between the intermediate quinonemethide and 2‐methylpropene whereas the latter may occur via a reaction related to a carbonyl‐ene reaction between the quinonemethide and 2‐methylpropene. Both compounds were subjected to a catalytic acidic treatment leading to 2,2‐dimethyl‐2 H ‐chromene. Starting from various salicylaldehydes, the scope of this method was investigated.