Stereoselectivity of halogenoboronation of phenylacetylene

Abstract

The halogenoboronation of phenylacetylene with boron trihalides (halogen = I, Br, or Cl) proceeds under kinetic control to produce dihalogeno-(Z)- or (E)-2-halogeno-2-phenylvinylboranes and (<10%) dihalogeno-(Z)- or (E)-2-halogeno-1-phenylvinylboranes. Subsequent reactions of these boranes with phenylacetylene produce halogenodivinyl- and trivinyl-boranes with the added acetylene substituting always as an (E)-2-halogeno-2-phenylvinyl ligand. The differences in reactivity of boranes formed by addition of boron at C-1 and -2 of the acetylene are discussed.