[2π + 2π]‐Photocycloadditionen in Bicyclo[2.2.2]octadien‐Derivaten

Abstract

(and ethylene) no other phototransformation of 14a takes place. With a half-life of ca. 12 min at 19°C the photoproduct 15a is thermally isomerized back to the diene diester 14a. Via a regiospecific addition of HCI, methanol and water to the tetracycles 15a and 15b (H2O) the epimeric products 18, 19 are isolated in a ratio of ca. 9: 1. Their structure is elucidated by oxidation of 18c to 21 and 'H-n.m.r. spectroscopic comparison with the isomeric compounds 20 and 22, resp., synthesized by a different route.Towards bishomodienophilic reagents like tetracyanoethylene and dimethyl acetylenedicarboxylate 15a shows the expected reactivity. The addition proceeds at the nonsubstituted edge of t h e bishomocyclobutadiene unit yielding 24 and 26.Bereits die ersten photochemischen Untersuchungen im Cyclohexa-1 ,CdienSystem 2 und den sich davon ableitenden 1,4-uberbruckten Homodienen 5 und 8 lieBen eine auffallende Divergenz im Reaktionsergebnis erkennen. In Derivaten des fast planaren Diens 2 konnte keine intramolekulare [2x + 2x1-Cycloaddition zu 1 erreicht werden; stattdessen lauft in der Regel eine Isomerisierung zu 3 ab2). Dem-

Photochemistry of Bridged and Unbridged Octaalkyl-Substituted syn-Tricyclo[4.2.0.02,5]octa-3,7-diene Derivatives

“…We also excluded 26 because compounds with the tetracyclo[4.2.0.0 2,8 .0 6,8 ]octane skeleton are unstable at room temperature. [18] Compounds 21 and 22 could each be isolated in about an 8 % yield. We rationalize their appearance by assuming the presence of 27 (Scheme 3) as an intermediate.…”

“…The main product was octamethylcuneane (19). As well as 6, the anti isomer of 1, octamethylcubane (18) was also found. The irradiation of 15 yielded a mixture of octaethylcubane (29) and octaethylcuneane (30), which could not be separated.…”

Towards In‐Plane Delocalized 4N/7e Radical Cations and 4N/6e Dications – One‐/Two‐Electron Oxidation of Proximate‐Parallel Bis(N,N'‐bicyclic)‐bishydrazines

“…It was in the context of our early interest in photochemical C=C/C=C cycloadditions as entry to synthetically versatile, high-energy cage compounds [48] that in-plane N=N/ N=N interactions and their photochemical exploitation had become an opportune project. As long ago as 1982, the synthesis and PE analysis of a first, truly proximate-parallel bisdiazene/bishydrazine was presented, [49] and over the years, a pool of structurally modified planar-parallel bisdiazenes has been added.…”

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

“…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…”