Photochemical Formation of Trans-Cyclohexene and Trans-Cycloheptene
Abstract
For nearly forty years, the transient existence of trans-cyclohexene has been postulated and believed to be accessible via UV-irradiation of cis-cyclohexene. Most text books suggest that trans-cyclooctene, which is the smallest trans-cycloalkene that has been prepared in pure form and is stable at room temperature,1 is the smallest that can be formed. Herein, we provide stereochemical evidence which supports the existence of trans-cyclohexene as well as our efforts to directly observe it with low temperature NMR. Furthermore, we demonstrate a practical method for the generation of the trans-cyclohexene utilizing blue LEDs, which provides facile access to a class of oxobicyclic structures currently inaccessible via thermal methods. In an example of uphill catalysis, a catalyzed reaction that is endergonic in nature, we synthesize the endergonic product, cyclohexanediol, via trans-cyclohexene which undergoes facile reversion to the cyclohexene when the light source is removed. These results suggest the possibility of a new class of chemical switch.Because trans-cycloheptene is a larger ring, it is less strained and has a longer life-time when compared to trans-cyclohexene. Consequently, trans-cycloheptene is more amenable to intermolecular chemical reactions. In the second project, we can generate trans-cycloheptene using blue LEDs, which provides facile access to a regio- and stereoselective access to a tricyclodiol which is a [2+2] dimer of the corresponding cycloheptenol.
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- OSU Theses [15752]