Substrate-Controlled\n[8 + 3] Cycloaddition of Tropsulfimides\nand Tropones with Zwitterionic Allenyl Palladium Species Derived from\nVinylidenecyclopropane-diesters

A palladium-catalyzed regioselective [8 + 3] cycloaddition\nof tropsulfimides\nand tropones with vinylidenecyclopropane-diesters (VDCP-diesters)\nhas been disclosed in this paper, affording decahydro-1<i>H</i>-cyclohepta[<i>b</i>]pyridine derivatives bearing an allene\nmoiety or decahydro-1<i>H</i>-cyclohepta[<i>b</i>]pyran derivatives having a conjugated diene unit in moderate to\ngood yields. The reactions proceed through a zwitterionic allenyl\npalladium species derived from VDCP-diesters. The substrate scopes\nhave been investigated and the plausible reaction mechanisms have\nalso been proposed according to the previous work, the first captured\nzwitterionic Pd-allenyl intermediate, and control experiments.