Radical cation photoisomerization of bicyclo[2.2.2]octa-2,5-diene to tetracyclo[4.2.0.02,8.05,7]octane and its thermal retrogression

Abstract

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Synthesis, characterization and computational evaluation of bicyclooctadienes towards molecular solar thermal energy storage

“…Methyl 2,2-dimethylbenzo[d] [1,3]dioxole-3a(7aH)-carboxylate (16, Scheme 1b) had previously been prepared by Paterson et al 26 and was provided to us for testing in the Diels-Alder reaction with 12. In this case the outcome was the same and 14 was again the favored product, indicating that the leaving group, methyl 2,2-dimethyl-1,3dioxole-4-carboxylate (18), was stable enough to drive the reaction towards byproduct formation. A new strategy for obtaining the BODs was thus necessary, and our idea was to instead perform the Diels-Alder reaction with an alkyne containing an acceptor group and a halogen, and thereafter to employ a cross-coupling reaction to introduce the donor group.…”

“…Upon irradiation, BODs can be converted to the corresponding photoisomer tetracyclooctane (TCO) (7). [15][16][17][18] The photophysical properties of BODs have been much less explored than other systems, one reason being that the photoisomer, TCO, is rapidly converted to BOD through thermal activation. Also, upon heating, BODs can degrade into an aromatic byproduct via a retro-Diels-Alder process and since the gaseous ethene is lost during the process, the reaction is irreversible (Scheme 1).…”

“…15 However, several examples of BODs and the corresponding TCOs have been isolated and reported in the literature . [15][16][17][18] For example, Gleiter et.al 19 described the formation of TCOs (Figure 2). The methyl estersubstituted (8) could not be isolated but proven by trapping with HCl, while 9 containing an epoxide functionality, could be isolated at 0 o C. TCO (10), with trifluoromethyl groups, was found to be more stable, with a half-life of 5.5 minutes at 80 o C. 19…”