Enantiopure double-helical phenylene ethynylene cyclophynes with the 2,2'-binaphthyl template.
New types of enantiopure compounds were synthesized to gain better insight into the structural features of phenylene ethynylene cyclophynes. Besides the previously obtained meta-substituted arylene ethynylenes, 1, ortho-connected phenylene ethynylene units were incorporated to give cyclophynes with ortho/meta and ortho/ortho connection modes, 2 and 3. Furthermore, a diphenylethyne component was also accommodated in 4. Both ab initio calculations and NMR spectra suggest a large amount of strain for 2 but less strain for 3 and 1 a, the latter having the smallest ring size among cyclophynes with the meta/meta connection mode. The CD spectra of 2 and 3 showed a characteristic shoulder at around 340 nm, similar to the case of 1 a. This implies that the aromatic acetylene bonds cross over each other in the double-helical structure. These results indicate that chirality information is useful for probing the persistency of molecular shape.
An
De-Lie
DL
Department of Chemistry, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, China. deliean@sina.com
Zhang
Ying-Jun
YJ
Chen
Qiang
Q
Zhao
Wen-Ying
WY
Yan
Hong
H
Orita
Akihiro
A
Otera
Junzo
J