- Guanidine–Copper Complex Catalyzed Allylic Borylation for the Enantioconvergent Synthesis of Tertiary Cyclic Allylboronates
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An enantioconvergent synthesis of chiral cyclic allylboronates from racemic allylic bromides was achieved by using a guanidine–copper catalyst. The allylboronates were obtained with high γ/α regioselectivities (up to 99:1) and enantioselectivities (up to 99 % ee), and could be further transformed into diverse functionalized allylic compounds without erosion of optical purity. Experimental and DFT mechanistic studies support an SN2′ borylation process catalyzed by a monodentate guanidine–copper(I) complex that proceeds through a special direct enantioconvergent transformation mechanism.
- Ge, Yicen,Cui, Xi-Yang,Tan, Siu Min,Jiang, Huan,Ren, Jingyun,Lee, Nicholas,Lee, Richmond,Tan, Choon-Hong
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supporting information
p. 2382 - 2386
(2019/02/01)
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- Catalytic enantioselective conjugate addition of Grignard reagents to cyclic enones using C1-1,1′-bisisoquinoline-based chiral ligands
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New highly constrained chiral C1-1,1′-bisisoquinoline ligands were examined in the enantioselective conjugate addition of Grignard reagents to cyclohexenone and cyclopentenone. The desired 1,4-adducts were obtained in excellent yield and moderate enantiomeric excess (up to 35%). Copyright Taylor & Francis Group, LLC.
- Qi, Gao,Judeh, Zaher M.A.
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experimental part
p. 1585 - 1592
(2012/05/04)
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- Pt-catalyzed oxidative rearrangement of cyclic tertiary allylic alcohols to enones using aqueous hydrogen peroxide
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An oxidative rearrangement of cyclic tertiary allylic alcohols to β-disubstituted α,β-unsaturated ketones by Pt black catalyst with aqueous hydrogen peroxide is described. The reaction proceeds under organic solvent- and halide-free conditions and gives only water as a coproduct. The Pt black catalyst is commercially available and can be reused at least four times.
- Nagamine, Takashi,Kon, Yoshihiro,Sato, Kazuhiko
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supporting information; experimental part
p. 744 - 746
(2012/09/22)
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- Stereoselective aziridination of cyclic allylic alcohols using chloramine-T
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The stereoselective aziridination of a range of cyclic allylic alcohols using two different chloramine salts (4-MeC6H4SO 2NClNa, TsNClNa and t-BuSO2NClNa, BusNClNa) has been explored. The stereoselectivity of these reactions was highly dependent on the structure of the allylic alcohol and the chloramine salt. Generally, mixtures of cis- and trans-hydroxy aziridines were obtained, in which the major diastereomer was the cis-hydroxy aziridine, whilst complete cis- diastereoselectivity was observed in the aziridination of 1,3-disubstituted allylic alcohols. In each case studied, aziridination using BusNClNa gave higher cis-stereoselectivity than that observed for the same reaction using TsNClNa. Unexpectedly, application of the aziridination conditions to 1-substituted cyclopen-2-en-1-ols did not generate the aziridines. Instead, epoxy sulfonamides were obtained.
- Coote, Susannah C.,O'Brien, Peter,Whitwood, Adrian C.
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supporting information; experimental part
p. 4299 - 4314
(2009/02/07)
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- Mechanism of the Grignard Adddition Reaction. XVI. Homolytic and Concerted Mechanisms in the Reaction of α,β-Unsatureted Carbonyl Compounds with Grignard Reagents
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Kinetic measurements have shown that the addition of Grignard reagents to α,β-unsaturated carbonyl compounds takes place either by a concerted mechanism or by a homolytic mechanism.Phenylmagnesium bromide, which is incapable of homolysis, reacts rapidly in a 1,4-fashion if an s-cis conformation exists between the C=C and the C=O bonds, but only 1,2-addition takes place if the conformation is s-trans.tert-Butylmagnesium bromide is unsuited to the concerted reaction, but 1,4-addition takes place via homolysis.Primary and secondary Grignard reagents, like phenyl, react rapidly in a concerted manner with s-cis substrates, but unlike phenyl, these Grignard reagents may, with s-trans substrates, produce some 1,4-adduct via the homolytic mechanism.
- Holm, Torkil
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p. 925 - 929
(2007/10/02)
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- Enantioselective Conjugate Addition of Grignard Reagents to Enones Catalyzed by Chiral Zinc(II) Complexes
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Various chiral zinc(II) complexes catalyze the asymmetric 1,4-addition of Grignard reagents to α,β-unsaturated ketones with high chemoselectivities (yields of 1,4-adducts, 83-99 percent), high regioselectivities (1,4/1,2 ratios up to 499) and modest enant
- Jansen, Johan F. G. A.,Feringa, Ben L.
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p. 4168 - 4175
(2007/10/02)
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- ORGANOMANGANESE (II) REAGENTS XI. A Study of their Reactions with Cyclic Conjugated Enones : Conjugate Addition and Reductive Dimerization
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The reaction of organomanganese reagents such as RMnX, R2Mn, R3MnLi and R3MnMgX with cyclohexenone has been studied.Two major pathways have been observed : conjugate addition and β reductive dimerization.Similar results have been obtained with organomagnesium compounds in presence of a catalytic amount of manganous salts.
- Cahiez, G.,Alami, M.
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p. 569 - 572
(2007/10/02)
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- CERIUM CHLORIDE-PROMOTED NUCLEOPHILIC ADDITION OF GRIGNARD REAGENTS TO KETONES AN EFFICIENT METHOD FOR THE SYNTHESIS OF TERTIARY ALCOHOLS
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In the presence of anhydrous cerium(III) chloride, Grignard reagents react with ketones to afford addition products in high yields, even though the substrates are susceptible to abnormal reactions with Grignard reagents alone.
- Imamoto, Tsuneo,Takiyama, Nobuyuki,Nakamura, Kamikazu
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p. 4763 - 4766
(2007/10/02)
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