Controllable Synthesis of Two Isomers 4H-Chromene and 2,8-Dioxabicyclo[3.3.1]nonane Derivatives under Catalyst-Free Conditions.

A one-pot method for the selective synthesis of two isomers 4H-chromene and 2,8-dioxabicyclo[3.3.1]nonane derivatives was developed without a catalyst and using EtOH/H2O (4:1, v/v) as the solvent. The reaction was conducted under mild conditions, with forming multiple chemical bonds in one pot and high atom economy, and only a stoichiometric amount of H2O is produced as the byproduct. Its selectivity was controlled by thermodynamics and kinetics, and the reasons for the transformation of the two structures are also discussed.