Direct Construction of the Chroman Structure from 1,3-Diene. Regioselective Protonation of Acyclic Polyene

The regioselective protonation of acyclic polyene was achieved, dependent on the choice of catalyst. The addition of myrcene to trimethylhydroquinone, using boron trifluoride–diethyl ether (1/1), predominantly gave a spiro structure. When (+)-10-camphorsulfonic acid was used as a catalyst, the major compound produced was chroman.