Ophirin synthesis

Natural Product Synthesis Using Grubb Metathesis Lasubine II, Ingenol, and Ophirin ... 

There are times that it is important to run the Grubbs reaction under equilibrating conditions. In the course of a synthesis of ophirin 12, Michael Crimmins of the University of North Carolina observed (J. Am. Chem. Soc. 2004,126, 10264) that metathesis of 8 under the usual conditions gave mainly the undesired cyclic dimer. At elevated temperature, the dimer re-entered the equilibrium, leading to the desired 9 as the major (15 1) product. The oxonene ring system of 10 then directed the intramolecular Diels-Alder cycloaddition, leading to 12. 

Grimmins, M.T, Brown, B.H., and Plake, H.R. (2006) An intramolecular Diels-Alder approach to the eimicellins enantioselective total synthesis of ophirin B and astrogorgin. /. Am. Chem. Soc., 128,1371-1378. 

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