Additions to Bromophenylethyne

Addition of IN₃ to bromophenylethyne (2) led to an unstable adduct 3, whose structure was indicated as 1-azido-2-bromo-2-iodo-l-phenylethyne by conversion to acetophenone. Hydration of 2 was also shown to proceed regiospecifically leading to phenacyl bromide, thus suggesting the intermediacy of an α-phenylvinyl-carbonium ion. Pyrolysis of IN₃ adduct 3 produced trans-dicyanostilbene (5) in 60% yield. Attempts to trap phenylcyanocarbene, a likely intermediate in this reaction, were unsuccessful. Reaction of 3 with aniline produced N,N′-diphenylbenzamidine (11) as the major product. The BrN₃ adduct of 2 also reacts with aniline to form 11. The likelihood of azirine intermediates in the above reactions is suggested.