Copper-Catalyzed Dehydrative Cyclization of 1-(2-Hydroxyphenyl)propargyl Alcohols with P(O)H Compounds for the Synthesis of 2-Phosphorylmethylbenzofurans

A tetrakis(acetonitrile)copper(I) hexafluorophosphate [Cu(MeCN)PF6]-catalyzed dehydrative reaction of 1-(2-hydroxyphenyl)propargyl alcohols with diarylphosphine oxides has been developed to provide an efficient synthesis of phosphorylated benzofurans in good to high yields. In the presence of a catalytic amount of an organic base, a variety of H-phosphonates and H-phosphinates can also be employed as good substrates to produce the corresponding products in moderate yields. The reaction has significant economical and ecological advantages since the formation of a new C(sp(3))-P bond and the benzofuran framework could both be achieved using an inexpensive copper catalyst with water produced as the sole by-product. Some synthetic transformations of the product have also been demonstrated.