New approaches to syntheses of diethers and haloethers from cyclopentadiene

Cyclopentadiene (CPD) is oxidized by copper(ii) bromide and chloride in alcohol solutions to form dialkoxy- and haloethers and exhibits a higher reactivity than butadiene. Dialkoxy-, chloroalkoxy-, and dichlorocyclopentenes are formed from CPD and CuCl₂ without catalysts. The reaction selectivity (yield of ethers calculated per consumed CuBr₂) reaches 98%. The characteristic feature of the oxidation mechanism is the parallel formation of all reaction products through a common intermediate (presumably, the bromonium cation) and bromine-containing carbocationic intermediates.