Oxadiazole polymer synthesis

H. Meng and W. Huang, Novel photoluminescent polymers containing oligothiophene and /u-phenylene-1,3,4-oxadiazole moieties synthesis and spectroscopic and electrochemical studies, J. Org. Chem., 65 3894-3901, 2000. 

Scheme 4. Synthesis of processible main chain oxadiazole polymers 14 (adapted from 36)...

Star-burst Oxadiazole Polymers. When a 1,3,5-trifunctional monomer is introduced in the synthesis (Scheme 8), a highly branched or star-burst polymer, or even a crosslinked polyaromatic oxadiazole may be expected to form according to the ratio of the monomers (45). A 1 1 1 ratio of 26 27 28 has been chosen to form a star-burst polyaromatic oxadiazole polymer 29. 

Scheme 8. Synthesis of a star-burst polyaromatic oxadiazole polymer 29 (adapted from 45)...

C. W. Spencer, F. Cacialli, J. Griiner, and R. H. Friend, Synthesis and optoelectronic properties of aromatic oxadiazole polymers, J. Chem. Soc. Chem. Commun. 7995 2211. 

From a medicinal chemist s point of view, oxadiazoles are among the most important heterocycles as they are one of the most commonly used bioisosters for amide and ester groups [67]. As such it is hardly surprising that the two regioisomeric oxadiazole scaffolds received the most interest in the field of microwave-assisted synthesis using polymer-supported reagents. 

Scheme 7.94 Synthesis of 1,3,4-oxadiazoles utilizing a polymer-bound Burgess reagent.

Fig. 7.8 Polystyrene-bound dehydrating agent (left) and polymer-supported phosphazene base PS-BEMP (right) utilized for oxadiazole synthesis.

The polymer-supported 5-chloromethyl-l,2,4-oxadiazole 162 undergoes easy reaction with primary amines to give the 5-aminomethyl oxadiazoles 163, which serve as excellent substrates for the synthesis of amides or sulfonamides 164 (Scheme 21 - yields not reported) <1999TL8547>. 

The use of polymer-supported reagents in combinatorial chemistry has received much attention in recent years, and a polymer-supported acylating reagent (supported on a ROMPGEL) has been used for the synthesis of 1,2,4-oxadiazoles in solution, (see Equation 37), <2000CCHT131>. 

J.J. Kim, K.-S. Kim, H.C. Kim, and M. Ree, Synthesis and properties of photoluminescent polymers bearing electron-facilitating oxadiazole derivative side groups, J. Polym. ScL, Part A Polym. Chem., 40 1173-1183, 2002. 

S.-Y. Zhang, F. Kong, R. Sun, R.-K. Yuan, X.-Q. Jiang, and C.-Z. Yang, Synthesis, characterization, and electro-optical properties of a soluble conjugated polymer containing an oxadiazole unit in the main chain, J. Appl. Polym. Sci., 89 2618-2623, 2003. 

J.A. Mikroyannidis and J.K. Spiliopoulos, Synthesis and optical properties of novel blue-light emitting poly(p-phenylene vinylene) derivatives with pendant oxadiazole and cyano groups, J. Polym. Sci., Part A Polym. Chem., 42 1768-1778, 2004. 

Kim TH, Kim HJ, Kwak CG, Park WH, Lee TS (2006) Aromatic oxadiazole-based conjugated polymers with excited-state intramolecular proton transfer their synthesis and sensing ability for explosive nitroaromatic compounds. J Polym Sci A Polym Chem 44 2059-2068... 

Oxadiazoles and their benzo derivatives find use in applications as diverse as pharmaceuticals, analytical reagents, propellants and explosives, starting materials in organic synthesis, and for polymer preparation and modification. 

The first report of the successful synthesis of high molecular weight PAEH by aromatic nucleophilic displacement reaction appears to be from the reaction of 2,5-di(4-fluorophenyl)-l,3,4-oxadiazole and 2,2-di(4-hydroxyphenyl)propane (bisphenol A) [1]. A polymer with a relative viscosity of 0.50 dL/g and a Tg of 180°C was obtained. The 1,3,4-oxadiazole unit activates the fluoro group sufficiently to allow displacement by the bisphenolate. The corresponding dichloro compound gave low molecular weight polymer. Another PAEH with a Tg of 180 °C and a crystalline melt temperature (Tm) of 250 °C was prepared from the reaction of 3,6-dichloropyridazine with bisphenol A [1]. 

Brain, C.T. and Brunton, S.A., Synthesis of 1,3,4-oxadiazoles using polymer-supported reagents, Synlett, 2001, 382-384. 

In the same publication, it was reported that this cyclo-dehydration could also be affected by using tosyl chloride and the polymer-supported phosphazene base PS-BEMP, and again, microwave heating was found to be advantageous (Scheme 6.25). In utilising this protocol, no scavenger purification strategy was deemed necessary and the authors note that this is the most efficient 1,3,4-oxadiazole synthesis of the three polymer-supported methods described. 

Brain, C.T., Paul, J.M., Loong, Y. and Oakley, P.J., Novel procedure for the synthesis of 1,3,4-oxadiazoles from 1,2-diacylhydrazines using polymer-supported Burgess reagent under microwave conditions, Tetrahedron Lett., 1999, 40, 3275. 

A one-step synthesis of 1,3,4-oxadiazoles from readily available carboxylic acids and acid hydrazides was mediated by the polymer-supported reagent... 

---