A Cu(I)-Xantphos system catalyzed the intramolecular hydroalkoxylation of unactivated terminal alkenes, giving five- and six-membered ring ethers. This system is applicable to both primary and secondary alcohols. A reaction pathway involving the addition of the Cu-O bond across the C-C double bond is proposed. A chiral Cu(I) catalyst system based on the (R)-DTBM-SEGPHOS ligand promoted enantioselective reaction with moderate enantioselectivity.
Phosphine organocatalysis enabled vicinal acylcyanation of alkynoates with acyl cyanides to form acrylonitrile derivatives with a tetrasubstituted alkene moiety. The acyl and cyano groups were introduced at the α and β carbon atoms, respectively, of the C-C triple bond in the alkynoates with complete regioselectivity and high anti stereoselectivity. A variety of functional groups in the acyl cyanides and alkynoates were tolerated.
Iridium-catalyzed enantioselective transfer hydrogenation of ketones with formic acid was developed using a prolinol-phosphine chiral ligand. Cooperative action of the iridium atom and the ligand through alcohol-alkoxide interconversion is crucial to facilitate the transfer hydrogenation. Various ketones including alkyl aryl ketones, ketoesters, and an aryl heteroaryl ketone were competent substrates. An attractive feature of this catalysis is efficient discrimination between the alkyl and aryl substituents of the ketones, promoting hydrogenation with the identical sense of enantioselection regardless of steric demand of the alkyl substituent and thus resulting in a rare case of highly enantioselective transfer hydrogenation of tert-alkyl aryl ketones. Quantum chemical calculations revealed that the sp 3-CÀ H/π interaction between an sp 3-CÀ H bond of the prolinol-phosphine ligand and the aryl substituent of the ketone is crucial for the enantioselection in combination with OÀ H•••O/sp 3-CÀ H•••O two-point hydrogen-bonding between the chiral ligand and carbonyl group.
A copper/prolinol-phosphine chiral catalyst enabled the one-step synthesis of chiral α-alkylidene-β-lactams. Optimization of the chiral ligand for steric and electronic properties realized the highly enantioselective coupling of nitrones and propargyl alcohol derived alkynes. The resulting chiral α-alkylidene-β-lactams served as a platform for various βlactams via well-established transformations of α,β-unsaturated carbonyl compounds.
The front cover picture, designed by three groups from Hokkaido (Japan: ramanus rose), Ibaraki (Japan: plum), and Ubon Ratchathani (Thailand: lotus) illustrates the enantioselective transfer hydrogenation reactions of ketones with formic acid under iridium catalysis. Rationally designed prolinol‐phosphine chiral ligands are highly effective for the hydrogenation of ketones including tert‐alkylaryl ketones in up to 99% yield and with up to 99.8% ee. DFT calculations showed non‐covalent interactions including O–H⋅⋅⋅O/sp3‐C–H⋅⋅⋅O two‐point hydrogen‐bonding and C–H/π interactions. Details of this work can be found in the communication on pages 4655–4661 (H. Murayama, Y. Heike, K. Higashida, Y. Shimizu, N. Yodsin, Y. Wongnongwa, S. Jungsuttiwong, S. Mori, M. Sawamura, Adv. Synth. Catal. 2020, 362, 4655–4661; DOI: 10.1002/adsc.202000615).
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