New Cobalt-Catalyzed Cycloisomerization of ε-Acetylenic β-Keto Esters. Application to a Powerful Cyclization Reactions Cascade

Abstract
The full details of investigations into the cobalt(I)-catalyzed ene type reaction of ε-acetylenic β-keto esters to form highly functionalized methylenecyclopentanes are described. The observed regio-, chemo-, and stereoselectivities support a process of cycloisomerization which controls the relative stereochemistry of two contiguous stereogenic centers. An efficient route to the basic skeleton of the phyllocladane family has been achieved via a one-pot sequence of cyclizations: ene type, [2 + 2 + 2], [4 + 2]. This new cascade created six carbon−carbon bonds and four rings in a totally stereoselective manner from an easily accessible acyclic polyunsaturated precursor.

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