Access to [6.4.0]carbocyclic systems by tandem metathesis of dienynes. A step toward the synthesis of a PreD3-D3 transition state analogue.

[reaction: see text] A new approach to the synthesis of linearly fused 6-8-6 tricarbocyclic systems, tandem ring-closing metathesis of dienynes, allows access to compounds with a carbon framework analogous to the proposed transition state of the isomerization of previtamin D(3) to vitamin D(3).