2647-03-2Relevant academic research and scientific papers
Determining the Enantiomeric Excess and Absolute Configuration of in Situ Fluorine-Labeled Amines and Alcohols by 19F NMR Spectroscopy
Jang, Sumin,Park, Hahyoun,Duong, Quynh Huong,Kwahk, Eun-Jeong,Kim, Hyunwoo
, p. 1441 - 1446 (2022/01/11)
The determination of the enantiomeric excess and absolute configuration of chiral compounds is indispensable in synthetic, pharmaceutical, and biological chemistry. In this article, we describe an efficient 19F nuclear magnetic resonance (NMR)-based analytical protocol for determining the enantiomeric excess and absolute configuration of in situ fluorine-labeled amines and alcohols. 2-Fluorobenzoylation was used to convert analytes to fluorinated amides or esters. The resulting F-labeled analytes were mixed with a cationic cobalt(III) complex, [Co]BArF, resulting in clean baseline peak separations of analyte enantiomers in 19F{1H} NMR spectra. The measured ΔδRS signs were unambiguously used to correlate the absolute configurations of amines, amino alcohols, and alcohols. Moreover, the structure-dependent 19F{1H} NMR signals enabled absolute configuration determination by analyzing the relative chemical shifts of enantiopure analyte samples with [Co]BArF and ent-[Co]BArF.
Copper-Catalyzed C(sp3)?H Amidation: Sterically Driven Primary and Secondary C?H Site-Selectivity
Bakhoda, Abolghasem (Gus),Jiang, Quan,Badiei, Yosra M.,Bertke, Jeffery A.,Cundari, Thomas R.,Warren, Timothy H.
supporting information, p. 3421 - 3425 (2019/02/14)
Undirected C(sp3)?H functionalization reactions often follow site-selectivity patterns that mirror the corresponding C?H bond dissociation energies (BDEs). This often results in the functionalization of weaker tertiary C?H bonds in the presence of stronger secondary and primary bonds. An important, contemporary challenge is the development of catalyst systems capable of selectively functionalizing stronger primary and secondary C?H bonds over tertiary and benzylic C?H sites. Herein, we report a Cu catalyst that exhibits a high degree of primary and secondary over tertiary C?H bond selectivity in the amidation of linear and cyclic hydrocarbons with aroyl azides ArC(O)N3. Mechanistic and DFT studies indicate that C?H amidation involves H-atom abstraction from R-H substrates by nitrene intermediates [Cu](κ2-N,O-NC(O)Ar) to provide carbon-based radicals R. and copper(II)amide intermediates [CuII]-NHC(O)Ar that subsequently capture radicals R. to form products R-NHC(O)Ar. These studies reveal important catalyst features required to achieve primary and secondary C?H amidation selectivity in the absence of directing groups.
