Facile Rearrangement of the 6,11-Diphenyldibenzo[b,f][1,4]diazocine Skeleton into a Substituted 2-(2-Aminophenyl)-1,3-diphenylisoindole via Anomalous Carbolithiation or Hydrolithiation: Corroboration of Operative SET Processes

Abstract

The starting 6,11-diphenyldibenzo[b,f][1,4]diazocine has been individually treated with R-Li reagents in THF, where R = AlH4, PhCH2, Ph2CH, Ph3C, CH3, CH3(CH2)3, C6H5 or Ph-C≡C, to learn whether an expected 1,2- or 1,4-addition would cleanly occur. Contrary to such an assumption based on nucleophilic attack, this [1,4]diazocine with PhCH2Li yielded only the enantiomers of (4b,11R)-11-benzyl-4b,11-diphenyl-4b,11-dihydro-5H-benzo[4,5]imidazo[2,1-a]isoindole; with Ph2CHLi yielded 2-[1-(4-benzhydrylphenyl)-phenyl-2H-isoindol-2-yl]analine; and with LiAlH4 2-(2-aminophenyl)-1,3-diphenylisoindole. Finally, individual reactions of the [1,4]diazocine with CH3Li, nBuLi or PhLi gave 4-5 inseparable products, instead of any simple 1,2 or 1,4 adduct. The anomalous carbolithiations and hydrolithiation observed are irreconcilable with a nucleophilic mechanism but in excellent accord with a SET radical-anion pathway.