Studies Towards Anti-Bredt Ring Systems of Natural Products

Different ways for the synthesis of anti-Bredt ring systems of natural products have been explored.

An intended Favorskii rearrangement-divinylcyclopropane rearrangement to lead to the bicyclo[4.3.1] decadiene ring system was not accomplished. An envisioned tandem cyclopropanation-divinycyclopropane rearrangement of 2,3-divinyhex-2-enol did not furnish the desired bicyclo[4.4.1]undecadiene system, either, because cyclopropane occurred on the exocyclic double bond.

In the course of cyclopropanation studies on various cyclohexenols, an α-silyl-α-diazoethyl acetate was employed as tether. It could be removed by protodesilylation or oxidative cleavage to give a 1-(carboxylic ester)-cyclopropane or a 1-(carboxylic easter)-1-hydroxy cyclopropane derivative, respectively. Cyclopropanation general occurred on the less substituted more electron rich double bond.

Epoxidation of 2,3-divinylhex-2-enol with subsequent Cope rearrangement furnished the anti-Bredt oxabicyclo[4.4.1]undecadiene system that could be transformed into its regioisomer by Ireland-Claisen rearrangement.

Studies of the ring-closing metathesis of a cobalt carbonyl complexed ynediene to give a 10- or 11-membered ring failed. Ring-closing metathesis of a vinylsilane furnished an eight-membered ring.