- A one-step synthesis of tetrahydropyranopyranones from carbonyl compounds
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A one-step synthesis of tetrahydropyranopyranones, a ring system present in the natural product FR182877, from carbonyl compounds is described.
- Armstrong, Alan,Goldberg, Fred W.,Sandham, David A.
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- Catalytic enantioselective nazarov cyclization: Construction of vicinal all-carbon-atom quaternary stereocenters
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The diastereoselective asymmetric synthesis of vicinal all-carbon-atom quaternary stereocenters is a challenging problem in organic synthesis for which only few solutions have been described. A catalytic asymmetric Nazarov cyclization of fully substituted dienones that provides cyclopentenone derivatives with vicinal quaternary stereocenters in high optical purity and as single diastereoisomers is now reported.
- Jolit, Anais,Walleser, Patrick M.,Yap, Glenn P. A.,Tius, Marcus A.
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supporting information
p. 6180 - 6183
(2014/06/23)
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- An efficient and enantioselective synthesis of d-biotin
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An efficient and enantioselective synthesis of d-biotin 1 starting from cis-1,3-dibenzyl-2-imidazo-lidone-4,5-dicarboxylic acid (6) is described. The key steps are the enantioselective reduction of meso-1,2-dicarboxylic thioanhydride 8 to prepare the (3as, 6ar)- thiolactone 9 and the introduction of the C6 side chain at C-2 in 9 via a modified Grignard reaction. This novel synthesis proceeded in six steps to afford 1 with 21% overall yield.
- Chen,Huang,Fu,Cheng,Zhang,Li,Peng
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p. 2004 - 2008
(2007/10/03)
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- CATHODIC SYNTHESIS OF CYCLOBUTANES
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Cathodic electrolysis of compounds with an activated methylene group in the presence of 1,3-dibromopropane affords 1,1-disubstituted cyclobutanes.
- Vasil'ev, A. A.,Tatarinova, V. I.,Petrosyan, V. A.
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p. 1221 - 1224
(2007/10/02)
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- Metal ion effects on the rate of intramolecular O-alkylation of the anion of ethyl(3-chloropropyl)acetoacetate
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The retarding effect of alkali metal and alkaline-earth metal ions on the rate of intramolecular O-alkylation of the title compound has been thoroughly investigated in 99% aqueous Me2SO at 25°C. Rate data have been dissected into contributions of free ions (ki) and ion pairs (kip). Comparison of the present results with available data for intramolecular C-alkylation of a strictly related system, reveals that rate-depressing effects due to cation pairing turn out to be remarkably similar in the two processes, which is at variance with the expectation of a more pronounced cation dependence of the kip/ki ratios for O-alkylation than for C-alkylation.
- Cacciapaglia, Roberta,Mandolini, Luigi
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p. 1353 - 1366
(2007/10/02)
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- Sensitized Photooxygenation. 3. Mechanistic Studies on the Singlet Oxygenation of 5,6-Disubstituted 3,4-Dihydro-2H-pyrans
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Studies on the photooxygenation of four 5,6-disubstituted 3,4-dihydro-2H-pyrans under singlet oxygen (1Δg) conditions are presented.For the 6-methyl-substituted substrates (1a,c), two hydroperoxides (2,3) are formed as the primary products, the ratio of which is solvent dependent, with the polar solvent favoring the production of 2.Hock cleavage of 5-hydroxyperoxide 2a and 2c is observed to occur via the possible intermediacy of dioxetane 4a and 4c.For the 6-phenyl analogue (1b,d), dioxetanes are observed to form directly, which decompose to ring-cleavageproducts (5b,d) readily. 6-Hydroperoxide 3a and 3c isomerize to 4-hydroperoxide 6a and 6c thermally, which further transform to 4-alcohol 7a and epoxy alcohols 8a and 8c.The singlet oxygenation reaction shows very significant effects of substitution and solvent.Both 6-phenyl and 5-acetyl substituents and polar solvents favor the "dioxetane-mode" process.Kinetic studies by the competition method indicate that the overall reaction rate decreases with increasing temperature, giving rise to a very significant negative enthalpy of activation.The experimental data is interpreted in terms of a prior formation of a reversible exciplex, which collapses to perepoxides, and the possible involvement of a zwitterionic transition state or intermediate along the "dioxetane" path.
- Chan, Yuk-Yee,Li, Xiaoyuan,Zhu, Chen,Liu, Xinhou,Zhang, Yuanda,Leung, Hiu-Kwong
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p. 5497 - 5504
(2007/10/02)
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- CYCLOALKYLATION BY THE α,ω-DIBROMIDES OF COMPOUNDS CONTAINING AN ACTIVATED METHYLENE GROUP AS A METHOD FOR THE SYNTHESIS OF 1,1-DISUBSTITUTED CYCLOALKENES
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A convenient preparative method was developed for the cycloalkylation of active methylene compounds, including β-diketones, by the dibromides BrCH2(CH2)nCH2Br (n = 0,1,2) in the presence of an excess of potassium carbonate in DMSO.The reaction gives high yields for the dibromides with n = 0 and 2, whereas the formation of cyclobutanes (n=1) is complicated by O,C-alkylation.The 1-substituted 1-acylcyclopropanes undergo thermal isomerization to the corresponding dihydrofuranes.
- Zefirov, N. S.,Kuznetsova, T. S.,Kozhushkov, S. I.,Surmina, L. S.,Rashchupkina, Z. A.
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p. 474 - 480
(2007/10/02)
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