A Greek cross dodecaphenylene: sparteine-mediated asymmetric synthesis of chiral D-2-symmetric pi-conjugated tetra-o-phenylenes

The asymmetric synthesis of a chiral, nonracemic pi -conjugated system with D-2 point group of symmetry, dodecaphenylene 4 is described. In the key st ep, (-)-sparteine- and Cu(II)-mediated oxidation of 2,2'-dilithio-1,1'-biar yls in ether gives the corresponding dimers, tetra-o-phenylenes, in 80% iso lated 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 bet ween 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 consis tent with significant conjugation between the four terphenyl moieties. (C) 2001 Elsevier Science Ltd. All rights reserved.