STEPWISE SYNTHESIS OF MAIN-CHAIN LIQUID-CRYSTALLINE MACROCYCLICS BASED ON CONFORMATIONALLY FLEXIBLE MESOGENS

A stepwise synthesis of ''main-chain'' regioirregular liquid-crystalli ne macrocyclic oligoethers based on conformationally flexible mesogens and flexible spacers is described, This method was applied to the syn thesis of the previously unreported cyclic trimer TPB'-(c)10(3), tetra mer TPB'-(c)10(4), and pentamer TPB'-(c)10(5), based on (4-hydroxyphen yl)-2(4-hydroxy-4'-biphenylyl)butane (TPB') and 1,10-dibromodecane. Th e method consists of the stepwise synthesis of the bisphenolic linear trimer of TPB' (5) and its phase-transfer-catalyzed etherification und er high dilution with 1,10-dibromodecane to yield the cyclic trimer TP B'-(c)10(3), The biselectrophilic linear monomer 6 and dimer 7 were se parated from a one step synthesis at high concentration, and their cyc lization with the bisphenolic linear trimer 5 at high dilution yielded the macrocyclic tetramer TPB'-(c)10(4) and respectively pentamer TPB' -(c)10(5), The unoptimized separated yields are up to 45%, making this synthetic method extremely valuable for preparative purposes, The pha se behavior of the macrocyclic liquid crystals based on TPB' (i.e., TP B'-(c)10(z) with z = 1-5) was compared with that of the corresponding macrocyclics based on the constitutional isomer 4-hydroxy-4'-biphenyly l)-2-(4-hydroxyphenyl)butane (TPB) [i.e., TPB-(c)10(z) with z = 1-5] w hich were prepared by a one-step synthesis, Advantages and disadvantag es of the stepwise versus one-step methods are discussed.