68664-23-3Relevant articles and documents
Tuning Triplet Energy Transfer of Hydroxamates as the Nitrene Precursor for Intramolecular C(sp3)-H Amidation
Chang, Sukbok,Jung, Hoimin,Keum, Hyeyun,Kweon, Jeonguk
supporting information, p. 5811 - 5818 (2020/04/10)
Reported herein is the design of a photosensitization strategy to generate triplet nitrenes and its applicability for the intramolecular C-H amidation reactions. Substrate optimization by tuning physical organic parameters according to the proposed energy transfer pathway led us to identify hydroxamates as a convenient nitrene precursor. While more classical nitrene sources, representatively organic azides, were ineffective under the current photosensitization conditions, hydroxamates, which are readily available from alcohols or carboxylic acids, are highly efficient in accessing synthetically valuable 2-oxazolidinones and γ-lactams by visible light. Mechanism studies supported our working hypothesis that the energy transfer path is mainly operative.
Iridium-Catalyzed Enantioselective C(sp3)-H Amidation Controlled by Attractive Noncovalent Interactions
Wang, Hao,Park, Yoonsu,Bai, Ziqian,Chang, Sukbok,He, Gang,Chen, Gong
supporting information, p. 7194 - 7201 (2019/05/10)
While remarkable progress has been made over the past decade, new design strategies for chiral catalysts in enantioselective C(sp3)-H functionalization reactions are still highly desirable. In particular, the ability to use attractive noncovalent interactions for rate acceleration and enantiocontrol would significantly expand the current arsenal for asymmetric metal catalysis. Herein, we report the development of a highly enantioselective Ir(III)-catalyzed intramolecular C(sp3)-H amidation reaction of dioxazolone substrates for synthesis of optically enriched γ-lactams using a newly designed α-amino-acid-based chiral ligand. This Ir-catalyzed reaction proceeds with excellent efficiency and with outstanding enantioselectivity for both activated and unactivated alkyl C(sp3)-H bonds under very mild conditions. It offers the first general route for asymmetric synthesis of γ-alkyl γ-lactams. Water was found to be a unique cosolvent to achieve excellent enantioselectivity for γ-aryl lactam production. Mechanistic studies revealed that the ligands form a well-defined groove-type chiral pocket around the Ir center. The hydrophobic effect of this pocket allows facile stereocontrolled binding of substrates in polar or aqueous media. Instead of capitalizing on steric repulsions as in the conventional approaches, this new Ir catalyst operates through an unprecedented enantiocontrol mechanism for intramolecular nitrenoid C-H insertion featuring multiple attractive noncovalent interactions.
Ruthenium(II)-Catalyzed Enantioselective ?-Lactams Formation by Intramolecular C-H Amidation of 1,4,2-Dioxazol-5-Ones
Xing, Qi,Chan, Chun-Ming,Yeung, Yiu-Wai,Yu, Wing-Yiu
supporting information, (2019/03/11)
We report the Ru-Catalyzed enantioselective annulation of 1,4,2-Dioxazol-5-Ones to furnish ?-Lactams in up to 97% yield and 98% ee via intramolecular carbonylnitrene C-H insertion. By employing chiral diphenylethylene diamine (dpen) as ligands bearing electron-Withdrawing arylsulfonyl substituents, the reactions occur with remarkable chemo- A nd enantioselectivities; the competing Curtius-Type rearrangement was largely suppressed. Enantioselective nitrene insertion to allylic/propargylic C-H bonds was also achieved with remarkable tolerance to the Ca?C and Ca‰iC bonds.