Novel Liquid Crystalline Compounds Containing Bicyclo[3.1.0]hexane Core Units

• Published in: European journal of organic chemistry 2004-01, Vol.2004 (2), p.289-303
• Main Authors: Kozhushkov, Sergei I., Langer, Rainer, Yufit, Dmitrii S., Howard, Judith A. K., Schill, Heiko, Demus, Dietrich, Miyazawa, Kazutoshi, de Meijere, Armin
• Format: Article
• Language: English
• Subjects: Cross-coupling; Cycloadditions; Liquid crystals; Small ring systems; Structure elucidation
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.200300448

Additions of ethyl or tert‐butyl diazoacetates to 4‐substituted cyclopentenes 6 and 17 under dirhodium tetraacetate/tetraoctanoate catalysis led to mixtures of tert‐butyl endo,exo‐ and exo,exo‐3‐carboxyl(aryl)bicyclo[3.1.0]hexane‐6‐carboxylates 7 and 18 in yields of 54−90% from which exo,exo‐diastereomers were isolated in yields of 39−63%. Diester exo,exo‐7 was saponified and converted into diaryl diesters exo,exo‐9a,b in overall yields of 42 and 46%, respectively. The esters exo,exo‐18 were reduced to the corresponding hydroxymethyl derivatives, these were transformed to the iodomethyl compounds which in turn were coupled with various alkylmagnesium halides, via Li2CuCl4 catalysis, to give 3‐aryl‐6‐alkylbicyclo[3.1.0]hexyl derivatives exo,exo‐21 in overall yields of 72−83%. Fluorinated 3‐(2‐arylethyl)‐6‐pentylbicyclo[3.1.0]hexane exo,exo‐32 could be prepared in five steps from 4‐ethoxy‐2,3‐difluorobenzaldehyde 26a adopting essentially the same synthetic strategy, but in an overall yield of only 8%, and 6‐(4‐cyanophenyl)‐3‐pentylbicyclo[3.1.0]hexane exo,exo‐38b was obtained by Pd(OAc)2 catalyzed cyclopropanation of 4‐pentylcyclopentene 34b with (4‐cyanophenyl)diazomethane 36b in 29% yield. A comparison of the liquid crystalline properties of these newly prepared compounds containing a bicyclo[3.1.0]hexane core with those of the known analogous compounds with a cyclohexane fragment shows that as a rule, a bicyclo[3.1.0]hexane moiety decreases the transition temperature, while the dielectric (Δϵ) and optical (Δn) anisotropies are comparable. However, the bicyclo[3.1.0]hexane unit has a poorer mesogenic potential. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)