Advances in Alkene and Alkyne Metathesis

As alkene metathesis is extended to more and more chaUenging substrates, improved catalysts and solvents are required. Robert H. Cirubbs ofCaltech developed (Organic Zeft. 2008, iO, 441) the diisopropyl complex 1, that efficiently formed the trisubstituted alkene 6 by cross metathesis of 4 with 5. Herve Clavier and Stephen P. Nolan of ICIQ, Tarragona, and Marc Mauduit of ENSC Rennes found J. Org. Chem. 2008, 73, 4225) that after cyclization of 7 with the complex 2b, simple filtration of the reaction mixture through sihca gel dehv-ered the product 8 containing only 5.5 ppm Ru. 

The merit of CH Cl as a solvent for alkene metathesis is that the catalysts (e.g. 1-3) are very stable. Claire S. Adjiman of Imperial College and Paul C. Taylor of the University of Warwick established Chem. Commun. 2008, 2806) that although the second generation Grubbs catalyst 3 is not as stable in acetic acid, for the cyclization of 9 to 10 it is a much more active catalyst in acetic acid than in CH Clj. Bruce H. Lipshutz of the University of California, Santa Barbara observed Adv. Synth. Cat. 2008, 350, 953) that even water could serve as the reaction solvent for the challenging cyclization of 11 to 12, so long as the solu-bihty-enhancing amphiphile PTS was included. 

Ernesto G. Mata of the Universidad Nacional de Rosario explored J. Org. Chem. 2008, 73, 2024) resin isolation to optimize cross-metathesis, finding that the acrylate 13 worked particularly well. Karol Grela of the Polish Academy of Sciences, Warsaw optimized (Chem. Commun. 2008, 2468) cross-metathesis with a halogenated alkene 16. 

Jeffrey S. Moore of the University of Illinois prepared J. Org. Chem. 2008, 73, 4256) a Mo alkyne metathesis catalyst on fumed silica gel that converted 28 to 29 at room temperature. The cyclization was driven by the vacuum removal of 3-hex5me 30. In the same paper. Professor Moore used the insolubility of a product diaryl alkyne 31 to drive other cyclizations. 

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