- Total Synthesis of ent-Pregnanolone Sulfate and Its Biological Investigation at the NMDA Receptor
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A unique asymmetric total synthesis of the unnatural enantiomer of pregnanolone, as well as a study of its biological activity at the NMDA receptor, is reported. The asymmetry is introduced by a highly atom-economic organocatalytic Robinson annulation. A new method for the construction of the cyclopentane D-ring consisting of CuI-catalyzed conjugate addition and oxygenation followed by thermal cyclization employing the persistent radical effect was developed. ent-Pregnanolone sulfate is surprisingly only 2.6-fold less active than the natural neurosteroid.
- Kapras, Vojtech,Vyklicky, Vojtech,Budesinsky, Milos,Cisarova, Ivana,Vyklicky, Ladislav,Chodounska, Hana,Jahn, Ullrich
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supporting information
p. 946 - 949
(2018/02/23)
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- Electrophilic cleavage of cyclopropylmethystannanes: An experimental comparison of σ-σ and σ-π conjugation
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(Chemical Equation Presented) Cyclopropylmethyltrimethylstannanes undergo electrophilic cyclopropane cleavage in chloroform with simple inorganic electrophiles (H+, SO2, I2) in a homologous reaction to the SE′ cleavage of allylic stannanes. The σ-σ conjugation between the carbon-tin bond and cyclopropane orbitals observed spectroscopically in the parent cyclopropylmethyltrimethylstannane is responsible for a rate enhancement of ca. 102 toward iodinolysis, relative to comparable alkyl stannanes. This acceleration is considerably less, however, than the ca. 109-fold rate enhancement provided by the corresponding σ-π conjugation in allylic stannanes. Methanol-tin coordination appears to reduce the activating influence of the metal, promoting methyl cleavage over cyclopropane fission with acid and iodine. Decreased σ-σ conjugation can also explain the decreased reactivity of cyclopropyltriphenylstannane compared with its trimethyltin counterpart. Cyclopropylmethylstannanes do not undergo the synthetically useful addition of aldehydes under conditions that facilitate the corresponding reaction of allylic stannanes.
- Lucke, Andrew J.,Young, David J.
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p. 3579 - 3583
(2007/10/03)
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- Regioselective Route to Sterically Hindered Cyclopropylcarbinyl Halides
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Reaction of cyclopropylcarbinyl alcohols 1 with hexachloroacetone and triphenylphosphine resulted in 80 - 90 percent yields of the corresponding cyclopropylcarbinyl chlorides 4 regioselectively, with no trace of the homoallylic chloride 2 or the chlorocyclobutane derivative 6a.Similar reaction of 1 with bromine and triphenylphosphine, in dimethylformamide, gave 65 - 80 percent yields of the cyclopropylcarbinyl bromide 5 with trace amounts of the homoallylic bromide 3 but no detectable bromocyclobutane derivative 6b.These reactions are amenable to the preparation of very sterically hindered cyclopropylcarbonyl halides, heretofore inaccessible, regioselectively and in a facile manner.
- Hrubiec, Robert T.,Smith, Michael B.
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p. 431 - 435
(2007/10/02)
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- AN IMPROVED, PREPARATIVE ROUTE TO 1-CYCLOPROPYL-1-HALOETHANES
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We wish to report a method for the synthesis of 1-cyclopropyl-1-chloroethane and 1-cyclopropyl-1-bromoethane, on a preparative scale, uncontaminated by 5-chloro(or bromo)-2-pentene.
- Hrubiec, Robert T.,Smith, Michael B.
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p. 593 - 600
(2007/10/02)
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- Ring-opening of Some Radicals containing the Cyclopropylmethyl System
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Mono- and bi-cyclic radicals containing the cyclopropylmethyl system are readily generated by interaction of the appropriate halides with triphenyl- or tributyl-stannane.Each radical studied underwent ring-opening by fission of the more substituted βγ-bond.In the case of the secondary radical (12b) the new double bond was formed preferentially in the trans-configuration.Rate constants, which cannot be determined with high accuracy by this method, lie in the range 1E7-3E8 s-1 at 25 deg C.When generated by the flow method in the e.s.r. cavity α-hydroxycyclopropylmethyl radicals undergo β-fission followed by 1,5-hydrogen atom t ransfer to afford enoxyl radicals.The latter reaction occurs more slowly in water than in non-polar solvents.The rigid hydroxynortricyclyl (43) undergoes preferential fission of the less substituted βγ-bond, possibly because of the dipolar nature of the transition state.
- Beckwith, Athelstan L. J.,Moad, Graeme
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p. 1473 - 1482
(2007/10/02)
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