Synthesis and structure of optically active helical poly- and oligocarbonates consisting of C2-chiral biphenyl unit

Enantiomerically pure (R)4,4',6,6'-tetramethyl-2,2'-dihydroxybiphenyl ((R)-6) and the corresponding cyclic carbonate were prepared along with racemic ones ((+/-)-6 and (+/-)-7). The X-ray crystallographic analysis of (+/-)-7 supported the proposed cyclic carbonate structure. Anionic ring-opening polymerization of cyclic carbonate (R)-7 with t-BuOK in THF gave thoroughly insoluble materials. Alternatively, soluble polycarbonate ((R)-5) with low molecular weight was synthesized by polycondensation of(R)-6. The model oligomers of (R)-5 (2 - 8mers) were synthesized (R)-5 exhibited large negative Cotton effect around 210 nm compared with that of its unit model ((R)-9) in the CD spectra. CD spectral study and structure simulation of the model oligomers ((R)-11 - 13) suggested that (R)-5 and higher oligomers can hold a stable left-handed helix in solution.