A Greek cross dodecaphenylene: sparteine-mediated asymmetric synthesis of chiral D2-symmetric π-conjugated tetra-o-phenylenes
作者:Andrzej Rajca、Hua Wang、Pavel Bolshov、Suchada Rajca
DOI:10.1016/s0040-4020(01)00241-1
日期:2001.4
The asymmetric synthesis of a chiral, nonracemic pi -conjugated system with D-2 point group of symmetry, dodecaphenylene 4 is described. In the key step, (-)-sparteine- and Cu(II)-mediated oxidation of 2,2'-dilithio-1,1'-biaryls in ether gives the corresponding dimers, tetra-o-phenylenes, in 80% isolated yields and 50-60% ee's. X-Ray crystallography confirms the structure of rac-4 and its molecular shape of a Greek cross. The torsional angles between the benzene rings in the tetra-o-phenylene core of rac-4 are in the 56.5-71.0 degrees range. However, CD and UV spectra of 4 in CH2Cl2 are consistent with significant conjugation between the four terphenyl moieties. (C) 2001 Elsevier Science Ltd. All rights reserved.