1,4-Dihydro-1,4-diarsinine: Facile Synthesis via Nonvolatile Arsenic Intermediates by Radical Reactions

Novel cyclic organodiarsenic compounds, 1,4-dihydro-1,4-diarsinines, were synthesized by radical reactions of pentamethylcyclopentaarsine (1) and acetylenic compounds. The radical reactions of 1 and acetylenic compounds such as dimethyl acetylenedicarboxylate (2a) and 4-ethynylpyridine (2b) in refluxing benzene with 2,2‘-azobis(isobutyronitrile) (AIBN; 5 mol %) under a nitrogen atmosphere provided the corresponding 1,4-dihydro-1,4-diarsinines (3). Formation of 1,4-dihydro-1,4-diarsinine was confirmed by 1H and 13C NMR spectra and FAB-mass spectrometry. The structures of 3 were confirmed as cis(e,e) forms by X-ray crystallography. This is a facile synthesis of cyclic organodiarsenic compounds, in which no volatile toxic intermediates such as arsenic chlorides and arsenic hydrides were used. Moreover, this is the first example of the synthesis of 1,4-dihydro-1,4-diarsinines.