- Erbium-Catalyzed Regioselective Isomerization-Cobalt-Catalyzed Transfer Hydrogenation Sequence for the Synthesis of Anti-Markovnikov Alcohols from Epoxides under Mild Conditions
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Herein, we report an efficient isomerization-transfer hydrogenation reaction sequence based on a cobalt pincer catalyst (1 mol %), which allows the synthesis of a series of anti-Markovnikov alcohols from terminal and internal epoxides under mild reaction conditions (≤55 °C, 8 h) at low catalyst loading. The reaction proceeds by Lewis acid (3 mol % Er(OTf)3)-catalyzed epoxide isomerization and subsequent cobalt-catalyzed transfer hydrogenation using ammonia borane as the hydrogen source. The general applicability of this methodology is highlighted by the synthesis of 43 alcohols from epoxides. A variety of terminal (23 examples) and 1,2-disubstituted internal epoxides (14 examples) bearing different functional groups are converted to the desired anti-Markovnikov alcohols in excellent selectivity and yields of up to 98%. For selected examples, it is shown that the reaction can be performed on a preparative scale up to 50 mmol. Notably, the isomerization step proceeds via the most stable carbocation. Thus, the regiochemistry is controlled by stereoelectronic effects. As a result, in some cases, rearrangement of the carbon framework is observed when tri-and tetra-substituted epoxides (6 examples) are converted. A variety of functional groups are tolerated under the reaction conditions even though aldehydes and ketones are also reduced to the respective alcohols under the reaction conditions. Mechanistic studies and control experiments were used to investigate the role of the Lewis acid in the reaction. Besides acting as the catalyst for the epoxide isomerization, the Lewis acid was found to facilitate the dehydrogenation of the hydrogen donor, which enhances the rate of the transfer hydrogenation step. These experiments additionally indicate the direct transfer of hydrogen from the amine borane in the reduction step.
- Liu, Xin,Longwitz, Lars,Spiegelberg, Brian,T?njes, Jan,Beweries, Torsten,Werner, Thomas
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p. 13659 - 13667
(2020/11/30)
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- Syntheses with organoboranes. VII, monohydroboration of conjugated dienes with catecholborane catalyzed by complexes of Nickel(II) chloride and Cobalt(II) chloride with diphosphines
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The monohydroboration of representative conjugated dienes 1-7 with catecholborane in the presence of SmI3, t-BuOSmI2, LaI3, Ti(OPr(i))4, iron(II), nickel(II) and cobalt(II) chloride complexes with dppe, dppp and dppb was examined. NiCl2(dppe), NiCl2(dppp) and CoCl2(dppp) shoned catalytic activity. The 1,2-addition products were obtained, no 1,4-addition was observed. The reactivity in the presence of NiCl2(dppe) decreased in the order acyclic dienes > cyclic dienes >>1-decene.
- Zaidlewicz, Marek,Meller, Jerzy
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p. 7279 - 7282
(2007/10/03)
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- Oxymetallation. Part 24. Preparation of cyclic peroxides by cycloperoxymercuriation of unsaturated hydroperoxides
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Seventeen unsaturated hydroperoxides have been converted by treatment with mercury(II) acetate and/or mercury(II) nitrate into nineteen new mercuriated cyclic peroxides and by subsequent demercuriation with alkaline sodium borohydride, six new mercury-free peroxides have been isolated. The results greatly extend the range of such reactions and provide information about the stereoselectivities and relative ease of several different modes of cycloperoxymercuriation. It is suggested that the reactions with mercury(II) acetate are kinetically controlled whereas those with mercury(II) nitrate show a component of thermodynamic control of product distribution.
- Bloodworth,Curtis,Spencer,Tallant
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p. 2729 - 2750
(2007/10/02)
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- The reaction of ketene-iminium ions with various olefins: A new preparation method for grandisol, fragranol and related dimethyl ethers
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We describe here the preparation of grandisol, fragranol and several related cyclobutanic by-products by procedures employing a [2+2] cycloaddition reaction between an olefine and a ketene-iminium cation generated in situ from an α-chloroenamine. The region- and stereospecificity of these cyclization reactions are studied.
- Grandguillot,Rouessac
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p. 5133 - 5148
(2007/10/02)
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- Exo- and Endohormones. X. A Novel Route to an Isomer Mixture of 7,9-Dodecadien-1-yl Acetate Utilizable in Field Attraction of Lobesia botrana Males
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Wittig condensation of (Z)-2-pentenylidene triphenylphosphorane (14) and 7-tert.-butoxy-heptanal (13) under conditions of phase transfer catalysis and subsequent conversion into the corresponding acetate afforded a mixture of 28percent 7(E),9(Z)-dodecadien-1-yl acetate, the sex pheromone of Lobesia botrana, along with the other geometrical isomers and 30percent unidentified by-products.The synthons 14 and 13 were prepared starting with (Z)-2-butene-1,4-diol (1) and hexane-1,6-diol (9), respectively.
- Daradics, L.,Oprean, I.,Hodosan, F.
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p. 277 - 282
(2007/10/02)
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- DIMETHYLALUMINUM CHLORIDE CATALYZED ENE REACTIONS OF ALDEHYDES.
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Dimethylaluminum chloride, which is a mild Lewis acid and a proton scavenger, catalyzes the ene reactions of aliphatic and aromatic aldehydes with alkenes containing a disubstituted vinylic carbon. Proton-initiated rearrangements do not occur, since the alcohol-Lewis acid complex formed in the ene reaction reacts rapidly to give methane and a nonacidic aluminum alkoxide. Formaldehyde and excess Me//2AlCl give good yields of ene adducts with all types of alkenes. With 1 equiv of Me//2AlCl, formaldehyde and mono- and 1,2-disubstituted alkenes give gamma -chloro alcohols resulting from cis addition of chlorine and hydroxymethyl groups to the double bond. This work is pertinent to the synthesis of alcohols.
- Snider,Rodini,Kirk,Cordova
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p. 555 - 563
(2007/10/02)
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- Total synthesis of (1RS,4SR,5RS)-4-(4,8-dimethyl-5-hydroxy-7-nonenyl)-4-methyl-3,8-dioxabicyclo[3.2.1] octane-1-acetic acid
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A method for the total synthesis of (1RS,4SR,5RS)-4-(4,8-dimethyl-5-hydroxy-7-nonenyl)-4-methyl-3,8-dioxabicyclo [3.2.1] octane-1-acetic acid is described. The compound is active as a utero-evacuant agent.
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- Total synthesis of the utero-evacuant substance d,l-zoapatanol
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A method of synthesizing 2S*,3R*-6E-(2-hydroxyethylidene)-2-methyl-2-(4,8-dimethyl-5-oxo-7-nonenyl)-oxepan-3-ol, one of the active ingredients in the zoapatle plant, is described. The active ingredients in the plant are useful as utero-evacuant agents.
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- Condensation de reactifs organomagnesiens sur les bromhydrines du type R-CH(Br)-CH2OH. Influence des sels cuivreux.
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Various allylic, vinylic and arylic Grignard reagents are able to condense with 2-bromo-1-alkanols in THF.The catalytic use of copper salts diminishes side reactions but is not required.
- Bourgain-Commercon, Monique,Normant, Jean F.
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p. 289 - 294
(2007/10/02)
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