Ag-Catalyzed Multicomponent Reaction To Access 9-Phosphorylated Xanthenes

This study describes an efficient multicomponent reaction of 2-hydroxybenzaldehyde, secondary phosphine oxides, and β-alkynyl ketones, which affords various 9-phosphorylated xanthenes in moderate to good yields under silver catalysis. The method is highly atom- and step-economical, representing a novel synthetic strategy for the construction of multisubstituted 9-phosphorylated xanthenes. Mechanistic studies of key intermediates indicate that the process proceeds via a sequence involving phospha-aldol, alkylation, cyclization, dehydration and cyclization.