Tandem Intramolecular Diels-Alder (Timda) Reactions: Branched Substrate Studies and New Synthetic Pathways

Abstract
Using a malonic ester route, the first branched tandem intramolecular Diels-Alder (TIMDA) precursor, 3, was synthesized from sorbic acid in seven steps (15% overall yield). Treatment with Lewis acid catalysts (e.g., boron trifluoride etherate) affects the TIMDA reaction to afford a new fused-tetracyclic, 4, as two diastereomers (1:1). An alternative synthetic route to key intermediates used in the synthesis of linear TIMDA precursors has also been achieved.