Synthesis of 2-Perfluoroalkyl 4H- and 2H-Chromenylphosphonates Mediated by Amines and Phosphines

An efficient synthesis of 2-perfluoroalkyl 4H-chromen-3-ylphosphonates 4a-i (R-F = CF3) and 5a-i (R-F = C2F5) has been accomplished via regioselective cycloaddition of 2-hydroxybenzaldehydes to diethyl 3,3,3-trifluoropropyn-1-yl- and diethyl 3,3,4,4,4-pentafluorobutyn-1-ylphosphonate, using trialkyl amines or phosphines as mediators. 2H-Chromen-3-ylphosphonates 6a-i were regioselectively obtained in the presence of triphenylphosphine. A convenient method for the isomerization of 4H-chromen-3-ylphosphonates into 2H-chromen-3-ylphosphonates 6a-i (R-F = CF3) and 7a-i (R-F = C2F5) was established.