- Enantioselective Desymmetrization of 2-Aryl-1,3-propanediols by Direct O-Alkylation with a Rationally Designed Chiral Hemiboronic Acid Catalyst That Mitigates Substrate Conformational Poisoning
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Enantioselective desymmetrization by direct monofunctionalization of prochiral diols is a powerful strategy to prepare valuable synthetic intermediates in high optical purity. Boron acids can activate diols toward nucleophilic additions; however, the design of stable chiral catalysts remains a challenge and highlights the need to identify new chemotypes for this purpose. Herein, the discovery and optimization of a bench-stable chiral 9-hydroxy-9,10-boroxarophenanthrene catalyst is described and applied in the highly enantioselective desymmetrization of 2-aryl-1,3-diols using benzylic electrophiles under operationally simple, ambient conditions. Nucleophilic activation and discrimination of the enantiotopic hydroxy groups on the diol substrate occurs via a defined chairlike six-membered anionic complex with the hemiboronic heterocycle. The optimal binaphthyl-based catalyst 1g features a large aryloxytrityl group to effectively shield one of the two prochiral hydroxy groups on the diol complex, whereas a strategically placed "methyl blocker"on the boroxarophenanthrene unit mitigates the deleterious effect of a competing conformation of the complexed diol that compromised the overall efficiency of the desymmetrization process. This methodology affords monoalkylated products in enantiomeric ratios equal or over 95:5 for a wide range of 1,3-propanediols with various 2-aryl/heteroaryl groups.
- Estrada, Carl D.,Ang, Hwee Ting,Vetter, Kim-Marie,Ponich, Ashley A.,Hall, Dennis G.
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- Selective catalytic sp3 C-O bond cleavage with C-N bond formation in 3-alkoxy-1-propanols
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The ruthenium catalyzed selective sp3 C-O cleavage with amide formation was reported in reactions of 3-alkoxy-1-propanol derivatives and amines. The cleavage only occurs at the C3-O position even with 3-benzyloxy-1-propanol. Based on the experimental results, O-bound and C-bound Ru enolate complexes were proposed as key intermediates for the unique selective sp3 C-O bond cleavage in 3-alkoxy-1-propanols.
- Chen, Cheng,Hong, Soon Hyeok
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supporting information; experimental part
p. 2992 - 2995
(2012/07/28)
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- Reductive cleavage of the C-O bond of acetals and orthoesters: Reduction by silane in the presence of a Rh-PPh3 complex
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Reductions of acetals to ethers and of orthoester to acetal by hydrosilane using rhodium catalyst are described.
- Ohta, Tetsuo,Michibata, Tsugumi,Yamada, Kazuyuki,Omori, Ryohei,Furukawa, Isao
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p. 1192 - 1193
(2007/10/03)
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- Synthesis of tetrahydroquinolines, hexahydrobenzoindolizines and an aryl phosphonate linker for the generation of catalytic antibodies
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Syntheses of 6-methoxy-1-methyl-1,2,3,4-tetrahydroquinoline-3-methanol 10 and 1,2,3,5,6,10b-hexahydrobenzo[g]indolizine-6-methanol 34 are described. The aryl phosphonic acid 14, which can be used as a linker to a protein, is synthesised and coupled to the above alcohols. These haptens, when linked to a protein, are intended to generate antibodies able to catalyse cationic cyclisation reactions.
- Gonzalez-Bello, Concepcion,Abell, Chris,Leeper, Finian J.
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p. 1017 - 1024
(2007/10/03)
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