Strained Trans Cyclic Alkenes

Undergraduate texts say the trans-cyclooctene is the smallest ring trans cycloalkene stable at room temperature. We are interested in these twisted double bond species in even smaller rings 6 and 7 membered rings. We are interested in these compounds and their derivatives because they represent limits in bonding. In other words how much strain can a double bond take and remain a double bond? What geometry do strained double bonds adopt? Can we use the strain energy inherent in these bonds as energy storage devices? Can we use the same strain energy to investigate reactive intermediates of reactions involving double bonds since these intermediates can now be produced at much lower temperatures? All of these questions are involved in this project.

Recently we have shown that trans to cis twisting barrier in trans-cycloheptene is much greater than had been previously assumed. In fact the instability of trans-cycloheptene is due to a bimolecular reaction producing a biradical which isomerizes to two cis cycloheptene molecules. This insight led us to synthesize geminally substituted trans-cycloheptenes I, which we have shown are stable to 130° - - the books are wrong! We have also used trans-cycloheptene to show that aziridinium intermediates (II) are, in fact, present in the ENE reaction and hope to extend this method examining intermediates in singlet oxygen addition to alkenes. Finally our results with trans cycloheptene suggest that trans-cyclohexenes (III) should also be observable using our methods.