1,1-Bi(trishomobarrelenyl) - Synthesis and Chiroptic Properties
1,1-Bi(endo,exo,syn-pentacyclo[3.3.3.02,4.06,8.09,11]undecyl)[1,1-bi(trishomobarrelenyl)] (4) has been prepared as a 1:1 mixture of its meso- and d,l-diastereomers in six steps from trishomobarrelene 1 via the amine 5, the N,N-bis(trishomobarrelenyl)sulfamide 6 and the 1,2-(trishomobarrelenyl)diazene 7 in 16 % overall yield. Crystals of meso-4 were grown from a pentane solution of the mixture and subjected to an X-ray structure analysis. The (+)- and the (-)-enantiomer were isolated by HPLC on a chiral-phase column. They exhibited significantly enhanced molar optical rotations which are consistent with the presence of three helically arranged 1,2-dicyclopropylethane units in their skeletons. The absolute configuration of the (+)-enantiomer was assigned on the basis of DFT computed optical rotations of both enantiomers to be all-(S).