A New Cyclization Reactions Cascade: Ene Type, [2 + 2 + 2], [4 + 2

The Behavior of 1,n-Enynes in the Presence of Transition Metals. Corinne Aubert, Olivier Buisine, and Max Malacria. Chemical Reviews 2002 102 (3), 813...
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J . Org. Chem. 1996,60,2664-2665

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Scheme 1

A New Cyclization Reactions Cascade:Ene Type, [2 2 23, [4 21. Stereoselective Formation of Six Carbon-Carbon Bonds and Four Rings in a One-Pot Sequence

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Paul Cruciani, Corinne Aubert, and Max Malacria* E' = CO&Hs ; E* = COCH3

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Received January 18, 1995

In recent years, transition metal-mediated cyclization of substrates containing two or more unsaturations have provided new catalytic strategies for the construction of complex polycyclic molecules.lV2 Toward this aim, we have disclosed a stereoselective approach3 to the basic framework of tetracyclic diterpenes of phyllocladane and kaurane families in a sequence involving three consecu21 tive cycloaddition reactions: a Pd(0)-assisted [3 annulation r e a ~ t i o n ,a~ [2 2 23 Co(1)-catalyzed cyclotrimerization,5 and finally, an intramolecular [4 + 21 cyclization. An ultimate goal of such an approach would be the discovery of a single transition metal mediating a onepot sequence of cyclizations.6 Our finding that Co(1) species catalyze the cycloisomerization of +acetylenic /?'alkyl /?-ketoesters with the diastereoselective generation of highly functionalized methylenecycl~pentanes~,~ suggested the feasibility of such a strategy: ene type reaction, [2 2 21, and [4 23 which would provide an unprecedented entry to substituted tetracyclic diterpenes. Here, we report an entirely novel and rapid access to the basic skeleton of the phyllocladane family via a onepot sequence catalyzed by (~5-cyclopentadienyl)dicarbonylcobalt(1) [CpCo(CO)2] creating six carbon-carbon bonds in a chemo-, regio-, and stereoselective manner (Scheme 1) from an acyclic polyunsaturated precursor owning three uncontrolled centers.

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Universitk Pierre et Marie Curie, Paris VI, Laboratoire de Chimie Organique de SynthBse, associk au CNRS, tour 44-54, B. 229, 4, Place Jussieu, 75252 - Paris Cedex 05, France

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