Transition-Metal-Catalyzed [3+2+2] Cycloaddition Reactions

[3+2+2] Cycloaddition reactions are of key importance in organic chemistry for the synthesis of seven-membered mono- and condensed carbocycles. This review article summarises the different reports on transition-metal-catalysed [3+2+2] cycloaddition reactions since 2000. Different transition-metals, such as Ni, Rh, Pd, Co, or Ru, which have been earlier reported for higher order [3+2+2] cycloaddition reactions are summarized in this article. The [3+2+2] cycloadditions of different functionalized substrates afford cycloheptane derivatives, 6-7,5-7 condensed bicyclic carbocycles, or 5-7-5 or 6-7-5 condensed tricyclic carbocycles. These higher order cycloaddition reactions may provide an easy route for the total synthesis of natural products, or as a preferable key synthetic step leading to final structure.