Synthesis of tribenzo-1,6-diazabicyclo[4.4.4]tetradecane

Abstract

1,6-Diazabicyclo[4.4.4]tetradecane, which was extensively studied by Alder et al. in the 1970–1980 s, exhibits very interesting redox and protonation properties. We intended to synthesize its benzo analog as an extension of our studies on aza cryptands; however, by following Alder’s synthetic route, we obtained only tricyclo[4.4.4.01,5]tetradecane tribenzo analog. Therefore, the target compound was synthesized from 2,11-diaza[3.3]-o-cyclophane. The proton-template synthesis of the benzo analog was straightforward and clean. The optimized structures of the products were obtained by DFT calculations since crystal structures were not available. The results showed that the NH+ proton of the ammonium salt was biased towards the nitrogen atom on one side. This is in contrast to the internally protonated 1,6-diazabicyclo[4.4.4]tetradecane·H+, in which the proton is located exactly halfway between two N atoms. Thus, the properties of the tribenzo analog is different from those of their parent aliphatic bicyclic diamine, and the basicity is comparable to that of ordinary amines.