Cesium Fluoride and Copper‐Catalyzed One‐Pot Synthesis of Benzoxazoles via a Site‐Selective Amide C−N Bond Cleavage

Abstract

We report herein a two-step one-pot strategy for the synthesis of benzoxazoles from amides by using cesium fluoride/copper as catalysts. This approach involves the in situ generation of acyl fluorides from the corresponding amides, and the acyl fluorides undergo transamidation and cyclization to give benzoxazoles in good yields. In this work, the amide CÀ N bonds are activated by CsF to form the acyl fluoride intermediates, which further react with o-bromoanilines to efficiently yield benzoxazoles. Notably, this methodology demonstrates a broad substrate scope, as primary/secondary benzamides are well tolerated, and this process might facilitate the development of one-pot transformations of amides. Scheme 5. Control experiments. Scheme 6. Preliminary mechanism studies. Scheme 7. Scale-up of the one-pot reaction.

Amide/Ester Cross-Coupling via C–N/C–H Bond Cleavage: Synthesis of β-Ketoesters

“…Some starting materials of amides were synthesized according to corresponding literature . Citations to the references containing characterization data for these compounds are given: 1a , 1b , 1c , 1d , 1f , 1i , 1k , 1n , 1o , 1p , 1a – a , 1a – c , 1a – d , 1a – e , 1a – f , 1a – g , 1a – h , 1a – i , 1a – j , 1a – k , 1a – l , 1a – m , 4a , 4d , 4c , 4f , and 4g …”

Non-Classical Amide Bond Formation: Transamidation and Amidation of Activated Amides and Esters by Selective N–C/O–C Cleavage

“…In 2018, the Zeng group applied their CsF-catalyzed transamidation to the synthesis of benzoxazoles via onepot, two-step tandem process involving CsF-catalyzed siteselective N-C(O) bond cleavage and Cu-catalyzed intramolecular cyclization (Scheme 28). 55 In this method, N,N-Boc 2activated 1° amides or N-Ts-activated 2° amides were treated with CsF and 2-haloanilines to afford transamidation products, which were then converted into benzoxazoles via intramolecular cyclization in the presence of Cu(I) catalysis. This method tolerates various amide and aniline substrates, affording benzoxazoles in good to excellent yields.…”

An efficient and straightforward approach for accessing thionoesters via palladium-catalyzed C–N cleavage of thioamides

“…Szostak, 40–57 Garg, 58–68 Zou, 69–71 Yamaguchi, 72–76 Huang, 77–83 Shi, 84–86 and Rueping 87–89 have made great contributions to the study of amide transformation. Our group 90–105 has also conducted excellent research in this field. As a thiocarbonyl analog of amide, it is extremely rarely reported that activated thioamide C–N bond cleavage formed various thio-compounds.…”