Transition metal catalyzed [2+2+2] cycloaddition and application in organic synthesis

The [2+2+2] cycloaddition strategy is complementary to the well known Diels-Alder reaction for the generation of polycyclic compounds. This [2+2+2] approach is atom-economical and, with the availability of new catalysts to effect the [2+2+2] cycloaddition reaction, synthesis of a wide variety of highly functionalized polycycles is possible. This review deals with some recent advances relating to [2+2+2] cycloaddition reactions involving the syntheses both of polycycles and of heterocycles. More specifically, syntheses of various biologically active molecules, unusual amino acids, and theoretically interesting molecules are described. An attempt has also been made to give an overview of recent advances in the achievement of chemo-, regio-, and stereoselectivity in cyclotrimerization reactions. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)