Abstract
The tetraketone 3,3,6,6‐tetramethylcyclohexane‐1,2,4,5‐tetrone (11) and its congener bicyclo[3.2.2]nonane‐6,7,8,9‐tetrone (17) were synthesized by conventional procedures. The photoreaction of 11 and 17 with tetramethylethylene yields 3,3,4,4,7,7,10,10‐octamethyl‐2,5‐dioxabicyclo[4.4.0]dec‐1(6)‐ene‐8,9‐dione (22) and 4,4,5,5‐tetramethyl‐3,6‐dioxatricyclo‐ [6.3.2.0^2;7^]tridec‐2(7)‐ene‐12,13‐dione (24), respectively. Both are formally diesters of a bishomosquaric acid. The interactions between the two nonconjugated diketone moities in 11 and 17 as well as between the donor and acceptor fragments in 22 and 24 were studied. X‐ray investigations of 11 and 17 show no deviation from the expected bond lengths and angles. In the case of 24 the distance between the carbon atoms of the donor and acceptor units is 2.39 Å, this is 0.11 Å shorter than the corresponding distance between the two acceptor units in 17. The PE‐spectroscopic investigations of 11 and 17 show a considerable interaction between the two acceptor units. This is concluded from the splitting of the PE bands (ca. 0.5 eV) of the four lone‐pair combinations. For 22 and 24 no interaction between the donor and acceptor part was detected by means of PE spectroscopy. The ^13^C‐NMR chemical data show a high‐field shift for the carbonyl carbon atoms in 11 and 17. These findings were substantiated by the investigation of the corresponding phenazine derivatives obtained from 11 and 17 by the reaction with o‐phenylenediamine. In the case of 22 and 24 a high‐field shift of the signals of the olefinic double bond was observed. The electronic absorption spectrum of 22 shows for the higher excited states a charge‐transfer contribution, whereas in the case of 24 a charge‐transfer contribution was already detected in the first excited state.