Regioselective Functionalization of the Oxazole Scaffold Using TMP-Bases of Mg and Zn
摘要:
A general method for the synthesis of 2,4,5-trisubstituted oxazoles has been developed. Starting from commercially available oxazole, successive metalations using TMPMgCl center dot LiCl or TMPZnCl center dot LiCl led to the corresponding magnesiated or zincated species which were stable toward ring fragmentation. Furthermore, they readily reacted with various electrophiles, such as aryl and allylic halides, acid chlorides, TMSCl, and TMS-CN, providing highly functionalized oxazoles.
Warming Up to Oxazole: Noncryogenic Oxazole Metalation and Negishi Coupling Development
作者:Michael J. Geier、Xiaotian Wang、Luke D. Humphreys、Selcuk Calimsiz、Mark E. Scott
DOI:10.1055/s-0037-1611909
日期:2019.9
details the development of several suitable noncryogenic metalation conditions for the synthesis of oxazole zincate. Subsequent rounds of high-throughput catalyst screening ultimately led to the identification of several suitable Pd sources that can be used for the Negishi coupling of unsubstituted oxazole. The scope and generality for one of the reported conditions is also presented.
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。