Conformational Analysis of Endoperoxides Grafted onto Bicyclo[2.2.n]alkanes as a Test of the Rigidity of the Bicyclic Skeleton. Photo‐oxidation of [2.2.2] Hericene and 2,3,5,6‐Tetramethylidenebicyclo[2.2.n]alkanes

Abstract

The photo-oxidation of [2.2.2]hericene (6) gave successively the endoperoxides 1 1 (9,10,11,12-tetramethylidene-4,S-dioxatricyclo[6.2.2.O2~7]dodec-2(7)-ene), the bis-endoperoxide 16 (1 5,16-dimethylidene-4,5,11,12-tetraoxatetracyclo[6.6.2.02~7.09~'4]hexadeca-2(7),9( 14)-diene), and the tris-endoperoxide 19 (4,5,11,12,17,18-hexaoxapentacyclo[6.6.6.02~7.09~'4.0'5~20]i~~~a-2(7),9( 14), 15 (20) with that reported for the ethylenetetracarbonitrile (TCNE) cycloadditions to the same polyenes. The rate-constant ratios k , / k , and k2/k3 for the three successive photo-oxidations of [2.2.2]hericene (6) did not differ significantly from unity, in contrast with the Diels-Alder additions of 6. Similarly, the rate-constant ratios k , / k , for the two successive photo-oxidations of tetraenes 7 and 8 were significantly smaller than those reported for the successive TCNE cycloadditions to 7 to 8. The endoperoxidc formations are not sensitive to the change in the exothermicity of the reactions but they are sensitive to the electronic properties (1P's)