Reaction Conditions for the Regiodivergent Direct Arylations at C2‐ or C5‐Positions of Oxazoles using Phosphine‐Free Palladium Catalysts
作者:Xinzhe Shi、Jean‐François Soulé、Henri Doucet
DOI:10.1002/adsc.201900641
日期:2019.10.22
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
据报道,恶唑的C 2或C 5的区域直接芳基化有两个反应条件。在这两种情况下,均使用无膦催化剂和廉价的碱,从而以中等至高收率获得芳基化的恶唑。使用Pd(OAc)2 / KOAc作为催化剂和碱,可观察到区域选择性C5-芳基化;而使用Pd(acac)2 / Cs 2 CO 3系统,芳基化发生在恶唑的C2位。与存在Pd(OAc)2 / KOAc系统时的C2-H键相比,恶唑的C5-H键具有更高的反应活性,这与协同的金属化去质子化机理是一致的。而C2芳基化可能是通过恶唑C2位的简单碱基去质子化。然后,从这些C2或C5芳基恶唑中,进行第二次钯催化的直接C H键芳基化,得到具有两个不同芳基的2,5-二芳基恶唑。我们还通过三个CH键功能化步骤将这些顺序的芳基化反应用于2-芳基菲[9,10- d ]恶唑的直接合成。还描述了2-芳基恶唑的芳基单元的Ru催化的CH芳基化。
N-Bromosuccinimide as a Brominating Agent for the Transformation of N-H (or N-Benzyl) Ketoaziridines into Oxazoles
作者:Heshmat Samimi、Farkhondeh Dadvar
DOI:10.1055/s-0034-1380518
日期:——
A novel procedure for the direct synthesis of 2,5-diaryloxazoles starting from N-H ketoaziridines is described. The method proceeds via the in situ formation of N-bromoketoaziridines in the presence of N-bromosuccinimide followed by the generation of intermediate azomethine ylides. A plausible mechanism for this transformation is proposed.
C–C Bond Cleavage of Keto-Aziridines; Synthesis of Oxazoles <i>via</i> Regio-Controlled Ring Expansion
作者:Heshmat Allah Samimi、Soraya Entezami
DOI:10.3184/174751913x13843364573005
日期:2013.12
The ring expansion of keto-aziridines to the corresponding 2,5-diaryloxazoles in the presence of iodine in refluxing dimethyl sulfoxide, is described. A plausible mechanism for the synthesis of 2,5-diaryloxazoles is proposed.
Iodine catalysed intramolecular C(sp<sup>3</sup>)–H functionalization: synthesis of 2,5-disubstituted oxazoles from N-arylethylamides
Iodine catalyzed synthesis of 2,5-substituted oxazoles from N-arylethylamides through intramolecular C(sp3)–H functionalization under metal-free conditions is described.