Palladium(II)-Catalyzed Intramolecular C–H Alkenylation for the Synthesis of Chromanes

The
intramolecular Pd­(II)-catalyzed alkenylation of aryl homoallyl
ethers constitutes a mild, versatile, and efficient procedure for
the synthesis of highly and diversely substituted chromanes and 2H-chromenes. The use of p-TsOH as an additive
allows more efficient reactions that could be carried out a room temperature
in most cases. The procedure has a wide scope, allowing the synthesis
of alkylidenechromanes and 2H-chromenes substituted
at C-2 or C-3 of the chromene moiety, thus accessing relevant flavenes
and isoflavenes, and even coumarins, in high yields (59 to 91%, 32
examples).