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. DOI: 10.1016/j.tetlet.2007.09.035) 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. DOI: 10.1021/ja074613o) 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. DOI: 10.1002/anie.200702186) 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. DOI: 10.1021/ol071402f) 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. DOI: 10.1021/ol7023554), 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. DOI: 10.1021/ja0746316) 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. DOI: 10.1021/jo0620617) 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. DOI: 10.1021/ja073573l) 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. DOI: 10.1021/ja071954t) 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. DOI: 10.1021/jo062546v) 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. DOI: 10.1002/anie.200703457) 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. DOI: 10.1021/ol702597y) Rh*-mediated enantioselective cyclopropanation of 28 to set the absolute configuration of (-)-pentalenene 32.