- Manganese catalyzed cis-dihydroxylation of electron deficient alkenes with H2O2
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A practical method for the multigram scale selective cis-dihydroxylation of electron deficient alkenes such as diethyl fumarate and N-alkyl and N-aryl-maleimides using H2O2 is described. High turnovers (>1000) can be achieved with this efficient manganese based catalyst system, prepared in situ from a manganese salt, pyridine-2-carboxylic acid, a ketone and a base, under ambient conditions. Under optimized conditions, for diethyl fumarate at least 1000 turnovers could be achieved with only 1.5 equiv. of H2O2 with d/l-diethyl tartrate (cis-diol product) as the sole product. For electron rich alkenes, such as cis-cyclooctene, this catalyst provides for efficient epoxidation.
- Saisaha, Pattama,Pijper, Dirk,Van Summeren, Ruben P.,Hoen, Rob,Smit, Christian,De Boer, Johannes W.,Hage, Ronald,Alsters, Paul L.,Feringa, Ben L.,Browne, Wesley R.
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supporting information; experimental part
p. 4444 - 4450
(2010/11/05)
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- The Synthesis of Glycols by Mercury-Photosensitized Alcohol Dehydrodimerization
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A variety of alcohols can be dehydrodimerized to give 1,2-diols on a multigram scale at 1 atm pressure and reflux temperature on photolysis (254 nm) in the presence of a trace of Hg vapor.Initial C-H bond breaking is followed by recombination of the resulting α-centered radicals, which normally leads to C-C bond formation α to oxygen.The reaction rate and selectivity can be increased by operating at lower temperatures under H2, in which case H atoms replace Hg* as the principal abstracting reagent and H atom abstraction from the α-CH bond leads directly to the α-C-centered radical.Under H atom conditions, unsaturated alcohols also react, in which case diols other than the 1,2-isomer can be formed selectively.The product can be rationalized on the basis of H atom addition to the C=C double bond to give the most stable radical which then dimerizes.For the special case of t-BuOH, H atom abstraction from the t-BuOH β-CH group under H atom conditions leads to the β-centered radical, which dimerizes to the 1,4-diol.Radical disproportionation accounts for some of the byproducts observed.The following previously unknown C-H bond strengths (kcal/mol) were determined from the results, assuming the literature BDE for the α-C-H of 2-propanol (91.0 +/-1.0); n-butanol, 92.8 +/- 1.0( α), 95.2 +/- 1.0 (β), and 94.3 +/- 1.0 (γ); n-propanol, 93.1 +/- 1.0 (α), and 95.0 +/- 1.0 (β), respectively.
- Lee, Jesse C.,Boojamra, Constantine G.,Crabtree, Robert H.
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p. 3895 - 3900
(2007/10/02)
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- Diethoxytriphenylphosphorane: A Mild, Regioselective Cyclodehydrating Reagent for Conversion of Diols to Cyclic Ethers. Stereochemistry, Synthetic Utility, and Scope
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Diethoxytriphenylphosphorane, Ph3P(OEt)2, prepared by reaction of triphenylphosphine and diethyl peroxide, is a "hydrolytically active" dioxyphosphorane which promotes mild cyclodehydration (40-110 deg C) of diols to cyclic ethers in neutral media.The regioselectivity in the closure of (S)-(+)-propane-1,2-diol and (R)-(-)-pentane-1,4-diol with Ph3P(OEt)2 is high (81-82 percent) while the cyclodehydration of (S)-(+)-phenylethane-1,2-diol gives racemized (+/-)-styrene oxide.Simple 1,2-, 1,4-, and 1,5-diols afford good yields of the cyclic ethers but 1,3-propanediol and 1,6-hexanediol give mainly 3-ethoxy-1-propanol and 6-ethoxy-1-hexanol, respectively with Ph3P(OEt)2.Tri- and tetra-substituted 1,2-diols afford the relatively stable 1,3,2-dioxaphospholanes (or ?-dioxyphosphoranes) in the presence of Ph3P(OEt)2, and, depending on conditions, the 1,3,2-dioxaphospholanes are selectively converted to epoxides, ketones or allylic alcohols.The carbonyl compounds arise from 1,2-hydride and 1,2-methyl migrations; the allylic alcohols are derived from thermolytic eliminations. trans-1,2-Cyclohexanediols afford essentially quantitative yields (>95 percent) of the cyclohexene oxides while cis-1,2-cyclohexanediol gives the stable 1,3,2-dioxaphospholane with Ph3P(OEt)2 which decomposes under thermal conditions to cyclohexanone (90 percent).Ph3P(OEt)2 is extremely useful for conversion of "sensitive" 1,2-diols to acidic and /or thermally labile epoxides as demonstrated by the quantitative conversion of 9,10-dihydro-trans-9,10-phenanthrenediol to 9,10-dihydrophenanthrene oxide and 2α,10-pinanediol to 2α,10-epoxypinane.
- Robinson, Philip L.,Barry, Carey N.,Kelly, Jeffery W.,Evans, Slayton A.
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p. 5210 - 5219
(2007/10/02)
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- PHOTOCHEMICAL REACTION OF ALCOHOLS-I IRRADIATION OF ALIPHATIC ALCOHOLS
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The UV irradiation of aliphatic alcohols gave α-glycols as the principal products.The values of the dl-α-glycol to meso-α-glycol ratios obtained in each example were analyzed.The stereochemical course of the formation of α-glycols, their conformations and configurations were established on basis of 1H NMR data.
- Balsells, R. Erra,Frasca, A. R.
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p. 245 - 255
(2007/10/02)
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- Desamination of β- and γ-Amino Alcohols
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Nitrous acid deaminations of the β-amino alcohols 2 and 12 afford 1,2 diols as well as ketones by pinacolic rearrangement.Both types of products arise with predominant inversion of configuration.Stereochemical studies and isotopic labeling reveal that formation of the diols involves an oxygen shift, presumably via oxirane intermediates.Deamination of the γ-amino alcohol 37 induces, in part, sequential rearrangements to give products also obtained from 12, but in different proportions and enantiomeric purities.Conformational control provides a reasonable explanation of our results.
- Guenther, Bernd-Rainer,Kirmse, Wolfgang
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p. 518 - 532
(2007/10/02)
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