Mechanism

In the transformation of compound 14 to compound 15, the reagents trimethylsilyl azide and triphenylphosphine were added to compound 14 in toluene. Through the first portion of the Staudinger reaction, the trimethylsilyl azide and triphenylphosphine react to produce the compound needed to react with the aldehyde of compound 14. Then, through the Wittig rearrangement, a rectangular intermediate is formed with the aldehyde. Triphenylphosphine oxide is lost in this step, and a retro-Aza-Claisen rearrangement occurs to form a primary aldimine. Another intramolecular rearrangement occurs to form the final 8-membered ring structure in compound 15.