Electronic Effect Directed Au(I)-Catalyzed Cyclic C2-H Bond Functionalization of 3-Allenylindoles

Gold-catalyzed cyclization reactions of indoles with an electron-deficient allene at the 3-position led to formation of dihydrocyclopenta[b]indole derivatives in moderate to excellent yields via C2-H bond functionalization of the indole unit. The presence of the electron-withdrawing alkoxycarbonyl, dialkoxyphosphono, or phenyl is crutial for this transformation. The potential synthetic dihydrocyclopenta[b]indole with the electron-withdrawing group has been demonstrated by applying a [3 + 2] cycloaddition reaction to construct the tretracycloskeleton.