Synthesis of phostones via DABCO-catalyzed bromocyclization of alkenylphosphonic acid monoesters

Abstract

The bromocyclization of 4-aryl-3-butenylphosphonic acid monoesters could proceed smoothly and rapidly in CH₃CN with 1.2 equiv. of NBS in the presence of 0.02 equiv. of DABCO at room temperature, giving exclusively the six-membered ring bromophostones with high endo regioselectivity but poor diastereoselectivity. The diastereomers were separated and their relative configurations were determined based on their NMR analysis and X-ray crystallography. Furthermore, we preliminarily demonstrated that the asymmetric bromocyclization of these kinds of substrates was possible.