Catalytic Staudinger/Aza-Wittig Sequence by in situ Phosphane Oxide Reduction

A Staudinger/aza‐Wittig reaction sequence is described that is catalytic in phosphorus. Towards this end, the phosphane oxide is reduced in situ by diphenylsilane, which allows for substoichiometric amounts of the catalyst 5‐phenyldibenzophosphole to be used. The substrate scope is investigated and benzoxazoles, benzodiazepine imidates and a 2‐methoxypyrrole were successfully synthesized. These investigations show that a fast aza‐Wittig reaction is required to obtain high yields. A catalytic Staudinger/aza‐Wittig reaction sequence, involving in situ phosphane oxide reduction, was successfully developed. Benzoxazoles, benzodiazepine imidates and 2‐methoxypyrrole were synthesized without phosphane oxide waste products.