Photoinduced Reaction of Triarylphosphines with Alkenes Forming Fused Tricyclic Phosphonium Salts

Herein
reported is a photoinduced reaction of triarylphosphines
with alkenes in the presence of carbonic acid. A drastic structural
change occurs to produce fused tricyclic phosphonium salts having
a phosphatricyclo­[4.3.0.02.9]­nonene core structure. The
reaction was marked by dearomatizing transannulation of the phenyl
ring, 1,2-migration of the phosphorus atom, and incorporation of an
alkene. The highly endergonic process is promoted by cooperation of
visible light with a photocatalyst under mild reaction conditions.