Double annulations of dihydroxy- and diacetoxy-dialkynylbenzenes. An efficient construction of benzodifurans

An efficient synthetic route to construct disubstituted benzodifurans from dihydroxy- or diacetoxy-dialkynylbenzenes utilizing Cs2CO3 or Pd(OAc)2/Cs2CO3 promoted double annulations is described. The scope for the reaction in the presence of a catalytic amount of Pd(OAc)2 is more general. In addition, it was observed that NaOH-promoted reaction of diacetoxy-dialkynylbenzenes may directly afford in THF/MeOH/H2O at 80 °C benzodifurans through hydrolysis and double cyclization in a one-pot manner. However, in most cases, the reaction is less selective affording a mixture of the double cyclization products and monocyclization–hydrolysis products.