- Simple phase transfer catalytic method for α-methoxylation of sterically hindered ketones
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Reactions of sterically hindered ketones of ArylCOCHR1R2 type (R1, R2 = Me, Et, Ph) with carbon tetrachloride and methyl iodide in the presence of solid KOH and 18-crown-6 afford the corresponding α-methoxyketones [ArylCOC(OMe)R1R2] in one-pot process in 30-67% yields.
- Abele,Rubina,Shymanska,Lukevics
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- Copper-Catalyzed Formation of α-Alkoxycycloalkenones from N-Tosylhydrazones
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The combination of 20 mol % of copper iodide and lithium tert-butoxide triggers the formation of a broad range of substituted, functionalized α-alkoxy 2H-naphthalenones from readily available N-tosylhydrazones. The data suggests that this transformation occurs through cycloaddition of a copper carbenoid with an ester, followed by a Lewis acid-catalyzed [1,2] alkyl shift of the in situ generated alkoxyepoxide intermediate. The combination of 20 mol % of copper iodide and lithium tert-butoxide triggers the formation of a broad range of substituted, functionalized α-alkoxy 2H-naphthalenones from readily available N-tosylhydrazones. The reaction proceeds by the cycloaddition of a copper carbenoid with an ester, and a subsequent Lewis acid-catalyzed [1,2] alkyl shift of the in situ generated alkoxyepoxide intermediate.
- Su, Naijing,Theorell, Juliana A.,Wink, Donald J.,Driver, Tom G.
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supporting information
p. 12942 - 12946
(2015/11/02)
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- Substituent Effects on the Strength of C-C Bonds, 14. - Kinetic and Thermodynamic Stability of 2,3-Bis(dialkylamino)-1,4-diketones - Energy of Stabilization of α-Dialkylamino α-Carbonylalkyl Radicals with Capto-dative Substituents
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The equilibrium constants and rate constants for the dissociation of the 2,3-bis(dialkylamino)-1,4-diketone diastereomers meso- and DL-7a and 7b were measured over a temperature range of 40 deg C.From the enthalpies of dissociation ΔHDiss and ethalpies of activation ΔH(excit.) and the strain enthalpies of 7 the bond dissociation enthalpies BDE(C-C) of 7 were determined.By comparison with the dissociation enthalpies of Ct-Ct alkanes the change of these BDEs(C-C) by the capto-dative substitution was determined to be 85.4 kJ mol-1 (20.4 kcal mol-1).The heats of formation ΔHf0(g) of a series of amino ketones 8 were determined from their heats of combustion and their heats of evaporation.From the ΔHf0(g) values in combination with MM2 calculations of their strain enthalpies strain-free increments CHn2-n> with n = 0, 1, 2 were derived and geminal interaction enthalpies in the ground states were obtained thereof.The radical stabilization enthalpy RSE of 6 was deduced from the ΔBDE(C-C) values and the ground state effect to be 73.6 kJ mol-1 (17.6 kcal mol-1).From these data and the radical stabilization enthalpies RSE of α-aminoalkyl radicals (4.2 kJ mol-1) and α-carbonyl radicals (28.9 kJ mol-1) a synergetic radical stabilization enthalpy of 40.5 kJ mol-1 (9.7 kcal mol-1) is deduced.This number combines "extra" resonance stabilization and general inductive or anomeric geminal substituent interaction in the radicals.The crystal structure of meso-7a has been determined by X-ray diffraction methods. - Key Words: C-C Bond cleavage, kinetics of / Heats of formation / Radicals, stability of / Capto-dative effect / Geminal substituents, energetic interaction of
- Welle, Frank,Verevkin, Sergej P.,Keller, Manfred,Beckhaus, Hans-Dieter,Ruechardt, Christoph
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p. 697 - 710
(2007/10/02)
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- Electrooxidative Cyclization of N-Acylhydrazones of Aldehydes and Ketones to Δ3-1,3,4-Oxadiazolines and 1,3,4-Oxadiazoles
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The electrolytic oxidation of ketone N-acylhydrazones (1) in methanolic sodium acetate induced their intramolecular cyclization to the corresponding 2-methoxy-Δ3-1,3,4-oxadiazolines 3.The thermal stability of a given oxadiazoline and what products were formed by its thermal decomposition was found to depend on the natures of the substituents at C-2.Thus, 2-methoxy-2-phenyloxadiazolines preferentially yielded oxiranes 5, whereas 2-alkyl-2-methoxyoxadiazolines preferentially gave enol ethers 6. 2,2-Dimethoxyoxadiazolines decomposed to the parent ketones and many unidentified products.The electrolytic oxidation of aldehyde N-acylhydrazones 2 gave 2,5-disubstituted 1,3,4-oxadiazoles 4.The oxidative cyclization of the N-benzoylhydrazones of aliphatic aldehydes gave especially high yields of the corresponding heterocycles.
- Chiba, Toshiro,Okimoto, Mitsuhiro
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p. 1375 - 1379
(2007/10/02)
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- Silver ion induced reactions of α-haloimines
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The silver ion induced reactions of α-haloimines are markedly different from similar reactions with the corresponding α-haloketones. The various reactions of α-haloimines, including α-alkoxylation 1,2-dehydrohalogenation, rearrangement via α-alkoxyaziridines, Favorskii-rearrangement and Wagner Meerwein rearrangement, are compared and evaluated with silver-induced reactions of α-haloketones The silver ion assisted reactions of α-haloimines are best interpreted in terms of the intermediacy c α-imidoylcarbenium ions or pseudo-α-imidoylcarbenium ions.
- De Kimpe, Norbert,Stevens, Christian
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p. 6753 - 6770
(2007/10/02)
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- Substituent effects on rates of formation of methoxy-substituted carbonyl ylides from 2-aryl-2-methoxy- an 5-aryl-2-methoxy-Δ3-1,3,4-oxadiazolines
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2-aryl-2-methoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazolines (4) and 5-aryl-2-methoxy-2,5-dimethyl-Δ3-1,3,4-oxadiazolines (5) were synthetized.Compounds 4 decompose in solution with first order kinetics.Rate constants are correlated with Hammett substituent constants (?-) with p(49.2 deg C) = 0.74 and 0.89 for CCl4 and CD3OD, respectively.The final products from 4 indicate that thermolysis involves the cleavage of both C-N bonds, to form N2 and initially, a carbonyl ylide.Compounds 5, which were obtained as mixtures of cis/trans isomers containing several impurities, and which therefore gave poorer kinetic data, decomposed in CDCl3 solution with p(45 deg C) = 1.1.Carbonyl ylide intermediates, similar to those from the closelyrelated compounds 4, were assumed on the basis of analogy and on the basis of partial identification of products.The effects of para substituents in the aryl groups of 4 and 5 show that the transition states have greater electron density at C-2 of 4 and at C-5 of 5 than do the starting materials.In spite of the increase in electron density at C-2 of 4, the transition state must be less polar, overall, than the ground state because rate constants for thermolysis of 4 in methanol are smaller than those for CCl4 solvent.A plausible explantation for the substituent effects and solvent effects in that the loss of N2 is concerted, with a transition state resembling more closely a spin paired 1,3-diradical than a 1,3-dipole.Alternative stepwise mechanisms, in which C2-N3 bond scission of 4 and C5-N4 bond scission of 5 are the rate-determining steps, leading to 1,5-diradical intermediates, can not be excluded on the basis of the evidence.
- Bekhazi, Michel,Smith, Peter J.,Warkentin, John
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p. 1646 - 1652
(2007/10/02)
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- Facile Synthesis of 2-Alkoxy-2-aryloxiranes
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Tertiary α-bromoalkyl aryl ketones 1 were converted into 2-alkoxy-2-aryloxiranes 4 exclusively by reaction with excess potassium carbonate in the corresponding dry alcohol.Silver carbonate in a dry alcohol with these α-bromo ketones yielded competitively formation of 2-alkoxyoxiranes and semi-benzilic Favorskii rearrangement (-> 5), while silver hexafluoroantimonate in the same medium afforded the latter rearrangement reaction exclusively.
- Kimpe, Norbert De,Buyck, Laurent De,Verhe, Roland,Schamp, Niceas
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p. 3631 - 3636
(2007/10/02)
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