Synthesis and fragmentation reactions of cyclic azo-compounds. Stereochemistry and transformations of photo-derived bicyclo[2,1,0]-pentanes, and thermal cycloreversion reactions of tricyclo[6,2,1,02,7]-undecatrienes and related compounds

Abstract

The potential for synthesis of syn and anti fused-ring bicyclo[2,1,0]pentanes by thermal and photochemical deazetation of polychlorodiazatetracyclo[6,2,1,13,602,7]dodeca-4,9-dienes and polychlorodiazatricyclo[6,2,1,02,7]-undeca-3,5,9-trienes prepared from common starting materials has been explored. Hitherto unknown types, endo,syn-polychlorotetracyclo[5,2,1,02,603,5]decenes have been made and their unusually rapid stereomutation into the endo–anti isomers studied kinetically. Polychlorinated examples of the hitherto unknown hydrocarbon types syn- and anti-tricyclo[4,3,01,607,9]nona-2,4-dienes have also been prepared; the ready thermal electrocyclic rearrangement of the anti-isomeric tricyclo[4,3,01,607,9]nonadiene has been observed to give the bicyclo[6,1,0]nonatriene system. In addition the ready thermal cycloreversion reactions of the previously postulated polychlorotricyclo[6,2,1,02,7]undeca-3,5,9-triene and the heterocyclic 9,10-diaza-analogue have been kinetically studied and the rate data compared to those for similar but more stable benzo-analogues. Novel reversible Diels–Alder cycloaddition of N-phenyltriazolinedione to the diene system in polychlorotricyclo[6,2,1,02,7]undeca-3,5,9-trienes is disclosed, and evidence for the intermediacy of polychloroisoindenes in cycloreversions of tricyclo[6,2,1,02,7]undeca-3,5,7,9-tetraenes presented. Many of these observations are rationalised in terms of orbital symmetry selected processes. Magnetic resonance data showing certain unusual features are discussed and attention is drawn to the use of second-order effects for assigning syn- and anti-stereochemistry to the fused ring bicyclo[2,1,0]pentanes; certain other unambiguous stereochemical assignments for bicyclo[2,2,1]heptane derivatives are made.