Rhodium-Catalyzed Sequential Cycloisomerization/Aldol Addition of Cyclopropene Carboxylic Acids with Isatins

A unique, rhodium-catalyzed reaction of cyclopropene carboxylic acids with isatins has been developed, which takes place through a trapping process of transient cyclic carboxylic oxonium ylides. This reaction tolerates a wide variety of cyclopropene carboxylic acids and N-protected or unprotected isatins and represents a new, direct strategy to access valuable γ-substituted γ-butenolide architectures containing an oxindole moiety in very high yields under mild reaction conditions.