- Organocatalytic, enantioselective intramolecular [6 + 2] cycloaddition reaction for the formation of tricyclopentanoids and insight on its mechanism from a computational study
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Diphenylprolinol silyl ether was found to be an effective organocatalyst for promoting the asymmetric, catalytic, intramolecular [6 + 2] cycloaddition reactions of fulvenes substituted at the exocyclic 6-position with a δ-formylalkyl group to afford synthetically useful linear triquinane derivatives in good yields and excellent enantioselectivities. The cis-fused triquinane derivatives were obtained exclusively; the trans-fused isomers were not detected among the reaction products. The intramolecular [6 + 2] cycloaddition occurs between the fulvene functionality (6π) and the enamine double bond (2π) generated from the formyl group in the substrates and the diphenylprolinol silyl ether. The absolute configuration of the reaction products was determined by vibrational circular dichroism. The reaction mechanism was investigated using molecular orbital calculations, B3LYP and MP2 geometry optimizations, and subsequent single-point energy evaluations on model reaction sequences. These calculations revealed the following: (i) The intermolecular [6 + 2] cycloaddition of a fulvene and an enamine double bond proceeds in a stepwise mechanism via a zwitterionic intermediate. (ii) On the other hand, the intramolecular [6 + 2] cycloaddition leading to the cis-fused triquinane skeleton proceeds in a concerted mechanism via a highly asynchronous transition state. (iii) The fulvene functionality and the enamine double bond adopt the gauche-syn conformation during the C-C bond formation processes in the [6 + 2] cycloaddition. (iv) The energy profiles calculated for the intramolecular reaction explain the observed exclusive formation of the cis-fused triquinane derivatives in the [6 + 2] cycloaddition reactions. The reasons for the enantioselectivity seen in these [6 + 2] cycloaddition reactions are also discussed.
- Hayashi, Yujiro,Gotoh, Hiroaki,Honma, Masakazu,Sankar, Kuppusamy,Kumar, Indresh,Ishikawa, Hayato,Konno, Kohzo,Yui, Hiroharu,Tsuzuki, Seiji,Uchimaru, Tadafumi
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supporting information; experimental part
p. 20175 - 20185
(2012/01/31)
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- Ring-chain tautomerism. Part 10 +. The reaction of oxocarboxylic acids with diazodiphenylmethane
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The rate coefficients for the esterification of a series of oxocarboxylic acids with diazodiphenylmethane have been determined in ethanol or 2-methoxyethanol at 30.0°C. These and the rates of reaction with model compounds have been used to estimate the equilibrium constants for ring-chain tautomerism for the oxocarboxylic acids.
- Bowden, Keith,Misic-Vukovic, Milica M.,Ranson, Richard J.
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p. 1601 - 1606
(2007/10/03)
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- Reactions of carbonyl compounds in basic solutions. Part 28. The alkaline hydrolysis of 2-formylbenzonitrile, N-(2-formyl and -acetylphenyl)acetamides, N-(2-formylphenyl)-substituted benzamides, 4-(2-formylbenzoyl)morpholine, 3-(4-morpholino)- and -(N-methylanilino)-phthalides and -na
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Rate coefficients have been measured for the alkaline hydrolysis of 2-formylbenzonitrile 1, N-(2-formyl and -acetylphenyl)acetamides 2, N-(2-formylphenyl)-3-substituted benzamides 3, 4-(2-formylbenzoyl)morpholine 4, 3-(4-morpholino)- and -(N-methylanilino)-phthalides 5 and -naphthalides 6 in 70percent (v/v) dioxane-water at various temperatures.The enthalpies and entropies of activation have been evaluated.The hydrolysis of the nitrile is second order in base and that of the amides is first order in base.The relative rates of hydrolysis, activation parameters and substituent effects have been used to suggest the mechanisms of the reactions.Intramolecular catalysis by the neighbouring carbonyl group occurs in the alkaline hydrolysis of 1-4.The alkaline hydrolysis of 5 and 6 is rapid due to their lactone structures.
- Bowden, Keith,Hiscocks, Simon P.,Reddy, M. Komal
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p. 1133 - 1138
(2007/10/03)
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- Formal transfers of hydride from carbon-hydrogen bonds. Attempted generation of H2 by intramolecular protonolyses of the activated carbon-hydrogen bonds of dihydrobenzimidazoles
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Protonolyses of carbon-hydrogen bonds can occur under suitable conditions to produce carbocations and H2. In an effort to accelerate these fundamental reactions, we have attempted to make them intramolecular by devising compounds in which carbon-hydrogen bonds designed to be particularly good formal donors of hydride are held in close proximity to acidic sites. Dihydrobenzimidazoles 4 and 11 are compounds of this type, since the carbon-hydrogen bonds at C2 are activated as formal donors of hydride by adjacent lone pairs in a dihydroaromatic ring, and acidic anilinium and carboxylic acid groups are held nearby. Unfortunately, this proximity does not lead to the formation of H2 by protonolysis; instead, other reactions intervene when compounds 4 and 11 are subjected to pyrolysis.
- Brunet,Wuest
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p. 689 - 696
(2007/10/03)
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