The cyclization of the dianions of 3-ketosulfones and cynotacetone with 1-bromo-2-chloroethane gives 2-alkylidenetetrahydrofuran which afforded functionalized ketosulfones and ketonitrile after BBr3-mediated cleavage. Diarlysulfides, diaryl ethers and biaryls were synthesized based on [3+3] cyclizations of 1,3-bis(silyl enol ethers) in an efficient way. The preparative scope of the new method for the synthesis of of 1-azaxanthones was expanded and a variety of new compounds were prepared in an efficient way. Furthermore, a new cyclization reaction of 3-thiophenoxy-1,3-diene with 1,1-diacylcyclopropanes was developed which provides a convenient approach to diarylsulfides containing a remote halide function. A number of new natural products were isolated from Symplocos racemosa Roxb and characterized by using various sophisticated spectroscopic techniques.
