Synthesis, Characterization, and Thermolysis of 7-Amino-7-azabenzonorbornadienes

Article abstract of DOI:10.1021/jo00246a031

Synthetic routes are given for the facile preparation of mono- and dibenzo-7-amino-7-azanorbornadienes 4 and 5.For 5 the key intermediate N-benzylisoindole (9) was treated with benzyne, generated via reaction of o-bromofluorobenzene with magnesium in THF to give tertiary amine 10.N-Bromosuccinimide-mediated debenzylation of 10 gave secondary amine 13, which was then aminated by O-(mesitylsulfonyl)hydroxylamine (MSH).Similarly amination of monobenzo amine 25 gave 4, which, however, proved to be unstable and therefore best isolated as the <(9-fluorenylmethyl)oxy>carbonyl (FMOC) derivative 27.Deblocking of 27 by means of diethylamine gave amine 4 as needed.Upon standing overnight in ether, free 4 underwent self-reduction to give dihydro derivative 29, whereas, in the presence of ethyl phenylpropiolate, cinnamate and dihydrocinnamate esters were formed.The simplest explanation for these results is that a reducing species is ejected upon thermolysis of 4.Nonstereospecific reduction occurred in contrast to the stereospecific reduction that occurred in the presence of authentic diimide precursor 23.Compounds 4 and 5 upon thermolysis in the presence of both acetic acid and propiolate ester led to stereospecific cis reduction.These results suggest that under acidic conditions protonated diimide is generated from both 4 and 5 whereas under neutral condotions 4 may yield azamine or a mixture of azamine and diimide.Direct involvement of 4 and 20 in reduction processes was, however, not eliminated.Thermolysis of 5 under neutral conditions is dependent on the solvent used.In DMF, clean conversion to 9,10-dihydroanthracene occurs whereas complex reaction mixtures are observed in benzene, chloroform, or THF.