Bromo-containing oxadiazoles in cross-coupling reactions

New mesomorphic 1,2,4-oxadiazoles containing o-, m-, and p-bromo-substituen ts have been synthesized and used as starting compounds in cross-coupling r eactions with arylboric acids. This procedure is widely used for synthesis of different biphenyls. For the first time we applied this method to the sy nthesis of heterocyclic compounds with five-membered oxadiazolic ring. As a result new liquid crystalline oxadiazoles of non linear structure were obt ained and characterized by NMR and mesomorphic phase transitions. The cross-coupling reaction with oxadiazoles containing a terminal p-Br-sub stituent easily provided as main products oxadiazole derivatives containing biphenyl fragments. On the contrary cross-coupling with m-bromo- and espec ially o-bromo-substituted oxadiazoles due to the steric hindrance was accom panied by a significant number of by-processes.