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Monday, January 23, 2012
Douglass F. Taber
University of Delaware

Advances in Alkene Metathesis: The Kobayashi Synthesis of (+)-TMC-151C

Shazia Zaman of the University of Canterbury and Andrew D. Abell of the University of Adelaide devised (Tetrahedron Lett. 2011, 52, 878. ) a polyethylene glycol-tagged Ru catalyst that is effective for alkene metathesis in aqueous mixtures, cyclizing 1 to 2. Bruce H. Lipshutz of the University of California, Santa Barbara developed (J. Org. Chem. 2011, 76, 4697, ; 5061, ) an alternative approach for aqueous methathesis, and also showed that CuI is an effective co-catalyst converting 3 to 5. Christian Slugovc of the Graz University of Technology showed (Tetrahedron Lett. 2011, 52, 2560. ) that cross metathesis of the diene 6 with ethyl acrylate 7 could be carried out with very low catalyst loadings. Robert H. Grubbs of the California Institute of Technology designed (J. Am. Chem. Soc. 2011, 133, 7490. ) a Ru catalyst for the ethylenolysis of 9 to 10 and 11.

Thomas R. Hoye of the University of Minnesota showed (Angew. Chem. Int. Ed. 2011, 50, 2141. ) that the allyl malonate linker of 12 was particularly effective in promoting relay ring-closing metathesis to 13. Amir H. Hoveyda of Boston College designed (Nature 2011, 471, 461. ) a Mo catalyst that mediated the cross metathesis of 14 with 15 to give 16 with high Z selectivity. Professor Grubbs designed (J. Am. Chem. Soc. 2011, 133, 8525. ) a Z selective Ru catalyst.

Damian W. Young of the Broad Institute demonstrated (J. Am. Chem. Soc. 2011, 133, 9196. ) that ring closing metathesis of 17 followed by desilylation also lead to the Z product, 18. Thomas E. Nielsen of the Technical University of Denmark devised (Angew. Chem. Int. Ed. 2011, 50, 5188. ) a Ru-mediated cascade process, effecting ring-closing metathesis of 19, followed by alkene migration to the enamide, and finally diastereoselective cyclization to 20.

In the course of a total synthesis of (-)-Goniomitine, Chisato Mukai of Kanazawa University showed (Org. Lett. 2011, 13, 1796. ) that even the very congested alkene of 22 smoothly participated in cross metathesis with 21, to give 23. En route to Leustroducsin B, Jeffrey S. Johnson of the University of North Carolina protected (Org. Lett. 2011, 13, 3206. ) an otherwise incompatible terminal alkyne as its Co complex 24, allowing ring closing methathesis to 25.

To construct the E alkene of (+)-TMC-151C (27), Susumu Kobayashi of the Tokyo University of Science extended (Angew. Chem. Int. Ed. 2011, 50, 680. ) the P.A. Evans silyl linker strategy. The conformational preference of the medium ring formed by the cyclization of 26 dictated the alkene geometry.

D. F. Taber, Org. Chem. Highlights 2012, January 23.