AZABULLVALENES AND BENZAZABULLVALENES . UNSATURATED HETEROCYCLIC SYSTEMS .60.

Submission of 7-azabicyclo[4.2.2]deca-2,4,9-trien-8-one (4) and 8-methoxy-7-azabicyclo[4.2.2]deca-2,4,7,9-tetraene (6) to ultraviolet irradiation, preferentially under conditions of acetone sensitization, results in photoisomerization to the azabullvalene system. The rearrangement appears to be general and has been applied to a number of congeners of 4 and 6. The variable-temperature nmr spectra of several azabullvalenes have been carefully examined. The observation has been made that although the vinyl and cyclopropyl protons do coalesce at the more elevated temperatures, the bridgehead proton maintains its identity throughout the averaging process. The unique rotational operations that can maintain the integrity of this proton are discussed in detail. The ground-state structures of the azabullvalenes are those in which the nitrogen atom is bonded to the bridgehead carbon atom. If the molecule possesses an additional methyl or methoxyl group, these substituents prefer to be bonded to a vinyl carbon. In cont ast to the earlier examples, benzazabullvalene 18 undergoes an irreversible reaction at 125-150°with the formation of a different benzazabullvalene (23). A mechanism which accommodates the observed double migration is presented. Attempts to prepare a complete unsubstituted azabullvalene have not yet been successful. Interestingly, however, lithium aluminum hydride treatment of amide 5 or methylthioaza-bullvalene (10) causes overreduction to bicyclic amine 25. A scheme is presented which accommodates the observed reactions and which is congruent with deuterium-labeling studies. Finally, the preparation of a 1:1 complex of methoxyazabullvalene and silver fluoroborate is described. © 1969, American Chemical Society. All rights reserved.