Zwitterionic Ring-Opened Oxyphosphonium Species from the Ph 3 P-I 2 Mediated Reactions of Benzo[ d ]oxazol-2(3 H )-ones with Secondary Amines.

Instead of the expected substituted 2-aminobenzo[ d ]oxazoles, relatively stable ring-opened oxyphosphonium betaines were isolated for the first time from the Ph ₃ P-I ₂ -mediated reactions of benzo[ d ]oxazol-2(3 H )-ones with acyclic secondary amines. The structure of one of these compounds was unambiguously confirmed by single-crystal X-ray analysis. Thermolysis of the betaines gave rise to 2-dialkylaminobenzoxazoles with concomitant loss of triphenylphosphine oxide, suggesting their possible role as intermediates in an alternative reaction path.