Stereochemistry of 2-substituted 5,6-benzo-1,3,2-dioxarsepines

1. 2-Chloro- and 2-bromo-5,6-benzo-1,3,2-dioxarsepines have the chair conformation with axial arrangement of the exocyclic bond at the arsenic atom. 2. In the case of 2-phenyl-, 2-(p-bromophenyl)-, and 2-(p-nitrophenyl)-5,6-benzo-1,3,2-dioxarsepines an equilibrium exists in solution between the chair-a and twist conformers, the ratio of which is close to unity.13C NMR spectra of "frozen conformers" at 143°K have been obtained for the first time for such a series of compounds. © 1985 Plenum Publishing Corporation