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Monday, August 18, 2008
Douglass F. Taber
University of Delaware

Transition Metal-Mediated Construction of Carbocycles: Dimethyl Gloiosiphone A (Takahashi), Pasteurestin A (Mulzer), and Pentalenene (Fox)

There continue to be new developments in transition metal- and lanthanide-mediated construction of carbocycles. Although a great deal has been published on the asymmetric cyclopropanation of styrene, relatively little had been reported for other classes of alkenes. Tae-Jeong Kim of Kyungpook National University has devised (Tetrahedron Lett. 2007, 48, 8014. ) a Ru catalyst for the cyclopropanation of simple α-olefins such as 1. X. Peter Zhang of the University of South Florida has developed (J. Am. Chem. Soc. 2007, 129, 12074. ) a Co catalyst for the cyclopropanation of alkenes such as 5 having elecron-withdrawing groups.

Alexandre Alexakis of the Université de Genève has reported (Angew. Chem. Int. Ed. 2007, 46, 7462. ) simple monophosphine ligands that enabled enantioselective conjugate addition to prochiral enones, even difficult substrates such as 8. Seunghoon Shin of Hanyang University has found (Org. Lett. 2007, 9, 3539. ) an Au catalyst that effected the diastereoselective cyclization of 10 to the cyclohexene 11, and Radomir N. Saicic of the University of Belgrade has carried out (Org. Lett. 2007, 9, 5063. ), via transient enamine formation, the diastereoselective cyclization of 12 to the cyclohexane 13. Alois Fürstner of the Max-Planck-Institut, Mülheim has devised (J. Am. Chem. Soc. 2007, 129, 14836. ) a Rh catalyst that cyclized the aldehyde 14 to the cycloheptenone 15.

Some of the most exciting investigations reported in recent months have been directed toward the direct diastereo- and enantioselective preparation of polycarbocyclic products. Rai-Shung Liu of National Tsing-Hua University has extended (J. Org. Chem. 2007, 72, 567. ) the intramolecular Pauson-Khand cyclization to the epoxy enyne 16, leading to the 5-5 product 17. Michel R. Gagné of the University of North Carolina has devised (J. Am. Chem. Soc. 2007, 129, 11880. ) a Pt catalyst that smoothly cyclized the polyene 18 to the 6-6 product 19. Yoshihiro Sato of Hokkaido University and Miwako Mori of the Health Science University of Hokkaido have described (J. Am. Chem. Soc. 2007, 129, 7730. ) a Ru catalyst for the cyclization of 20 to the 5-6-5 product 21. Each of these processes proceeded with high diastereocontrol.

Transition metal-mediated polycarbocyclic construction has also been applied to natural product synthesis. Takashi Takahashi of the Tokyo Institute of Technology has developed (J. Org. Chem. 2007, 72, 3667. ) the Pd-mediated spirocyclization of 22 to 23, leading to a formal synthesis of dimethyl gloiosiphone A (24). Johann Mulzer of the Universität Wien employed (Angew. Chem. Int. Ed. 2007, 46, 9320. ) the Vollhardt cyclization of 25 to 26 in an enantioselective synthesis of pasteurestin A (27). In a particularly straightforward approach, Joseph M. Fox of the University of Delaware used (Org. Lett. 2007, 9, 5625. ) Rh*-mediated enantioselective cyclopropanation of 28 to set the absolute configuration of (-)-pentalenene 32.

D. F. Taber, Org. Chem. Highlights 2008, August 18.