Efficient Synthesis of Novel 1,3,4-Oxadiazoles Bearing a 4-N,N-Dimethylaminoquinazoline Scaffold via Palladium-Catalyzed Suzuki Cross-Coupling Reactions.

Barbara Wołek,Mateusz Werłos,Magdalena Komander,Agnieszka Kudelko

doi:10.3390/molecules25215150

Abstract

Two series of novel (symmetrical and unsymmetrical) quinazolinylphenyl-1,3,4-oxadiazole derivatives were synthesized using palladium-catalyzed Suzuki cross-coupling reactions. The presented synthetic methodology is based on the use of bromine-substituted 2-phenyl-4-N,N-dimethylaminoquinazolines and either a boronic acid pinacol ester or a diboronic acid bis(pinacol) ester of 2,5-diphenyl-1,3,4-oxadiazole. The reactions are conducted in a two-phase solvent system in the presence of catalytic amounts of [1,1′-bis(diphenylphosphino)ferrocene]-dichloropalladium(II), sodium carbonate, and tetrabutylammonium bromide, which plays the role of a phase-transfer catalyst. The luminescence properties of the obtained compounds are discussed in the context of applying these compounds in optoelectronics. Specifically, two highly-conjugated final products: N,N-dimethyl-2-phenyl-6-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)quinazolin-4-amine (8f) and 6,6′-(4,4′-(1,3,4-oxadiazole-2,5-diyl)bis(4,1-phenylene))bis(N,N-dimethylquinazolin-4-amine (9f), which contain a 1,3,4-oxadiazole moiety connected to a quinazoline ring by a 1,4-phenylene linker at the 6 position, exhibit strong fluorescence emission and high quantum yields.

Highlights

Heterocyclic compounds containing five-membered diazole or six-membered diazine scaffolds have recently attracted attention due to the fact that they participate in a wide range of biological interactions and have potential for various industrial applications
1,2,4-triazole cores cores conjugated conjugated novel organic or 1,2,4-triazole via via phenylene phenylene linker linker to to different different homohomo- and and heteroaromatic heteroaromatic arrangements, arrangements, which which resulted resulted in in the the generation of products generation of products with with high high fluorescence fluorescence quantum quantum yields yields [53]. Building upon upon these these results results involving monomers for for potential applications, involving novel novel conjugated conjugated diazole-derived diazole-derived monomers potential optoelectronic optoelectronic applications, we describe the combination of two different individual structural motifs (i.e., 1,3,4-oxadiazole we describe the combination of two different individual structural motifs (i.e., 1,3,4-oxadiazole and Suzuki cross-coupling cross-coupling reaction and quinazoline) quinazoline) using using aa phenylene phenylene linker linker via via aa palladium-catalyzed palladium-catalyzed Suzuki reaction
2a-g were were prepared prepared in in aa two-step two-step synthesis synthesis according according to to methodologies methodologies described in the literature

Summary

Introduction

Heterocyclic compounds containing five-membered diazole or six-membered diazine scaffolds have recently attracted attention due to the fact that they participate in a wide range of biological interactions and have potential for various industrial applications. B and C virus (HBV, HCV) inhibitors [3,4], anticancer drugs (zibotentan), and as antimicrobial (furamizole) [4,5], antifungal [4,6], and antiallergic agents [7]. Because of their favorable thermal and luminescent properties, compounds based on the 1,3,4-oxadiazole ring are candidates for optoelectronic materials, including organic light emitting diodes (OLEDs) [8,9], liquid crystals [10], metal ion sensors [11,12], and coordination polymers [13]. Some reports have described (i) oxidative cyclization of N-acylhydrazones with different oxidizing agents, such as Dess-Martin periodinane (DMP) [17], N-chlorosuccinimide (NCS)

Methods

Results

Conclusion