126773-86-2

Upstream product

• 288-42-6 oxazol 
• 3972-65-4 1-bromo-4-tert-butylbenzene 
• 105359-79-3 2-(4-(tert-butyl)phenyl)-4,5-dihydrooxazole 
• 1710-98-1 p-tert-butyl benzoyl chloride 
• 126773-85-1 5-Bromo-2-(4-tert-butylphenyl)oxazole 

Relevant academic research and scientific papers

Reaction Conditions for the Regiodivergent Direct Arylations at C2- or C5-Positions of Oxazoles using Phosphine-Free Palladium Catalysts

Two sets of reaction conditions for the regiodivergent C2- or C5- direct arylations of oxazole are reported. In both cases, phosphine-free catalysts and inexpensive bases were employed allowing the access to the arylated oxazoles in moderate to high yields. Using Pd(OAc)2/KOAc as catalyst and base, regioselective C5-arylations were observed; whereas, using Pd(acac)2/Cs2CO3 system, the arylation occurred at the C2-position of oxazole. The higher reactivity of C5-H bond of oxazole as compared to the C2-H bond in the presence of Pd(OAc)2/KOAc system is consistent with a concerted metalation deprotonation mechanism; whereas the C2-arylation likely occurs via a simple base deprotonation of the oxazole C2-position. Then, from these C2- or C5-arylated oxazoles, a second palladium-catalyzed direct C?H bond arylation affords 2,5-diaryloxazoles with two different aryl groups. We also applied these sequential arylations to the straightforward synthesis of 2-arylphenanthro[9,10-d]oxazoles via three C?H bond functionalization steps. The Ru-catalyzed C?H arylation of the aryl unit of 2-aryloxazoles is also described. (Figure presented.).

Direct arylation of oxazole and benzoxazole with aryl or heteroaryl halides using a palladium-diphosphine catalyst

Through the use of PdCl(dppb)(C3H5) as a catalyst, a range of aryl bromides and chlorides undergoes coupling via C-H bond activation/functionalization reaction with oxazole or benzoxazole in good yields. This air-stable catalyst can be used at low loadings with several substrates. Surprisingly, better results in terms of substrate/catalyst ratio were obtained in several cases using electron-excessive aryl bromides than with the electron-deficient ones. This seems to be mainly due to the relatively low thermal stability of some of the 2-arylbenzoxazoles formed with electron-deficient aryl halides. With these substrates, in order to obtain higher yields of product, the reactions had to be performed at a lower temperature (100-120 °C) using a larger amount of catalyst. On the other hand, in the presence of the most stable products, the reactions were performed at 150 °C using as little as 0.2 mol% catalyst. Arylation of benzoxazole with heteroaryl bromides also gave the coupling products in moderate to high yields using 0.2-5 mol% catalyst. With this catalyst, electron-deficient aryl chloride such as 4-chlorobenzonitrile, 4-chloroacetophenone or 2-chloronitrobenzene have also been used successfully.

Synthesis of 2-Aryl- and 5-Alkyl-2-aryloxazoles from 2-Aryl-5-bromooxazoles

2-Aryloxazoles, their 5-deuterio derivatives, and 5-alkyl-2-aryloxazoles are prepared in good yields from 2-aryl-5-bromooxazoles via halogen/metal exchange with butyllithium followed by treatment with water, methanol-O-d, or alkyl halides, respectively.