Cobalt-Catalyzed Chemo- and Enantioselective Hydrogenation of Conjugated Enynes
Asymmetric hydrogenation is one of the most powerful methods for the preparation of single enantiomer compounds. However, the chemo- and enantioselective hydrogenation of the relatively inert unsaturated group in substrates possessing multiple unsaturated bonds remains a challenge. We herein report a protocol for the highly chemo- and enantioselective hydrogenation of conjugated enynes while keeping the alkynyl bond intact. Mechanism studies indicate that the accompanying Zn2+ generated from zinc reduction of the CoII complex plays a critical role to initiate a plausible CoI/CoIII catalytic cycle. This approach allows for the highly efficient generation of chiral propargylamines (up to 99.9 % ee and 2000 S/C) and further useful chemical transformations.
Synthesis of substituted benzo[: B] [1,4]oxazepine derivatives by the reaction of 2-aminophenols with alkynones
We have developed a novel synthetic method accessing benzo[b][1,4]oxazepines that are one of the rare classes of benzoxazepine derivatives by reaction of 2-aminophenols with alkynones in 1,4-dioxane at 100 °C. A series of benzo[b][1,4]oxazepine derivatives can be prepared by using this synthetic protocol. Mechanistic experiments indicated that the hydroxy proton of the aminophenol could play a crucial role in the formation of an alkynylketimine intermediate that undergoes 7-endo-dig cyclization.
Bisphosphine catalyzed sequential [3 + 2] cycloaddition and Michael addition of ynones with benzylidenepyrazolones: Via dual α′,α′-C(sp3)-H bifunctionalization to construct cyclopentanone-fused spiro-pyrazolones
A bisphosphine-catalyzed sequential [3 + 2] cycloaddition and Michael addition reaction of ynones with benzylidenepyrazolones has been developed. Under the catalysis of DPPB [1,4-bis(diphenylphosphino)butane], the reaction proceeded smoothly to give spiro-[cyclopentanone] pyrazolone derivatives in moderate to good yields with good diastereoselectivities via sequential dual α′,α′-C(sp3)-H bifunctionalization annulation. This strategy provides a novel route toward the synthesis of spiro-[cyclopentanone] pyrazolones containing three contiguous stereocenters which possess potential pharmaceutical activities.
Zhang, Jiayong,Miao, Zhiwei
supporting information
p. 9461 - 9471
(2019/01/03)
Enantioselective Cyanosilylation of Alkynyl Ketones Catalyzed by Combined Systems Consisting of Chiral Ruthenium(II) Complex and Lithium Phenoxide
Asymmetric cyanosilylation of alkynyl ketones with the catalyst systems consisting of amino acid/2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP)/ruthenium(II) complex and lithium phenoxide (Ru?Li cat.) was studied. The reaction was conducted in tert-butyl methyl ether (TBME) at ?78 °C with a substrate-to-catalyst molar ratio (S/C) as high as 2000. A series of simple and functionalized ketones was converted into the alkynyl tertiary cyanohydrin derivatives in up to 99% ee. Appropriate selection of an amino-acid ligand of the catalyst according to the substrate structure was crucially important to achieve high enantioselectivity and a wide scope of substrates. Transformation of the chiral cyanohydrin product into a functionalized lactone was also examined. (Figure presented.).