## 5 Direct Arylation of 1,3,4-Oxadiazoles Using Compounds Bearing Different Functionalities  
Other methods for the direct arylation of oxadiazole rings that have been described in the literature in the last decades are presented below. Among these methods, only a few can be defined as universal procedures because in most cases, researchers received only one 1,3,4-oxadiazole derivative (Scheme 8 [61-62] and Scheme 9 [71-79]). Thus, 2-phenyl-1,3,4-oxadiazole was used as the starting reagent in the synthesis of the following conjugated derivatives: 5,5\({}^{\prime}\)-diphenyl-2,2\({}^{\prime}\)-bi(1,3,4-oxadiazole) (Scheme 8, **22**) [61], 2,5-diphenyl-1,3,4-oxadiazole (Scheme 8, **23**) [62], 2-(5-methoxythiophen-2-yl)-5-phenyl-1,3,4-oxadiazole (Scheme 8, **24**) [63], 2-(benzo[d]thiazol-2-yl)-5-phenyl-1,3,4-oxadiazole (Scheme 8, **26**, **29**) [65,68], 2-phenyl-5-(4-methylphenyl)-1,3,4-oxadiazole (Scheme 8, **28**) [67], 3-(5-phenyl-1,3,4-oxadiazol-2-yl)-\(N\)-(quinolin-8-yl)thiophene-2-carboxamide (Scheme 8, **30**) [69], and 2-(4-methoxyphenyl)-5-phenyl-1,3,4-oxadiazole (Scheme 8, **31**) [70] via direct arylation It was also used to synthesize 2,5-di(naphthalene-1-yl)-1,3,4-oxadiazole (Scheme 9, **32**) [71], 3-(5-phenyl-1,3,4-oxadiazol-2-yl)-\(N\)-(quinolin-8-yl)thiophene-2-carboxamide (Scheme 9, **34**) [73], 2-phenyl-5-(3-(trifluoromethylphenyl)phenyl)-1,3,4-oxadiazole (Scheme 9, **35**) [74], 2,5-diphenyl-1,3,4-oxadiazole (Scheme 9, **36**) [75], 2-(6-(4-methoxyphenyl) naphthalene-2-yl)-5-phenyl-1,3,4-oxadiazole derivative (Scheme 9, **39**) [78], and also 2,5-diphenyl-1,3,4-oxadiazole (Scheme 9, **40**) [79]. The most frequently used catalysts in the presented direct arylation reactions of 1,3,4-oxadiazole derivatives include salts of Pd, Cu, Co, and Ni. They are most often accompanied by phosphine-complexing ligands. The transformations are usually carried out at high temperatures (110-140 \({}^{\circ}\)C) in different polar or non-polar solvents for relatively long reaction times. In 2012, [PERSON] and co-workers published a versatile method for the direct desulfitative arylation of 2-aryl-1,3,4-oxadiazoles at the C2 position using sodium benzenesulfinate. This procedure produced the corresponding 2,5-diaryl-1,3,4-oxadiazole derivatives in high yields (Scheme 8; **25a-e**; 79-95%) [64]. In the same year, [PERSON] et al. reported the deamidative arylation of 1,3,4-oxadiazoles through a tandem decarbonylation and C-H functionalization sequence. The starting substrates were 2-aryl-1,3,4-oxadiazoles and \(N\)-methoxy-4-methylbenzamide, which were converted into 2,5-diphenyl-1,3,4-oxadiazole derivatives in satisfactory yields (Scheme 8; **27a-c**; 77-85%) [66]. Another work by [PERSON] et al. described the use of disulfides bearing a pyrimidine moiety in a C-C cross-coupling reaction with 2-aryl-1,3,4-oxadiazoles, which led to a series of ethyl 4-methyl-2-(5-phenyl-1,3,4-oxadiazol-2-yl)pyrimidine-5-carboxylates (Scheme 9; **33a-e**; 68-75%) [72]. In 2019, [PERSON]'s group used 1-aryltriazenes as the arylating source for the C-H functionalization of 2-aryl-1,3,4-oxadiazoles (Scheme 9; **37a-c**; 77-84%) [76]. In 2021, [PERSON] and co-workers published a method for the biaryl coupling of the 2-aryl-1,3,4-oxadiazole moiety and bipyridine derivatives (Scheme 9; **38a-d**; 50-66%) [77]. **Scheme 8. Direct conversation of 2-aryl-1,3,4-oxadiazoles into corresponding 2,5-diaryl-1,3,4-oxadiazoles from 2010 to 2014. **  
**Scheme 9. Direct conversation of 2-aryl-1,3,4-oxadiazoles into corresponding 2,5-diaryl-1,3,4-oxadiazoles 2015 to 2022. **  
**6. Direct Arylation of 1,3,4-Oxadiazoles by Condensation**  
An interesting group of methods for the formation of 2,5-diarylsubstituted 1,3,4-oxadiazoles is direct condensation reactions involving the addition of a 1,3,4-oxadiazolecore to an unsaturated arrangement and the subsequent elimination of low-molecular-weight by-products.