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Ketone addition ring closure

Muna Ahmed Mohamed El Hadi, Feng-Jie Zhang, Fei-Fei Wu, Chun-Hua Zhou, Jun Tao
Fruits produce a range of volatile compounds that make up their characteristic aromas and contribute to their flavor. Fruit volatile compounds are mainly comprised of esters, alcohols, aldehydes, ketones, lactones, terpenoids and apocarotenoids. Many factors affect volatile composition, including the genetic makeup, degree of maturity, environmental conditions, postharvest handling and storage. There are several pathways involved in volatile biosynthesis starting from lipids, amino acids, terpenoids and carotenoids...
2013: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Jennifer Ciesielski, Vincent Gandon, Alison J Frontier
A study of the reactivity and diastereoselectivity of the Lewis acid promoted cascade cyclizations of both acyclic and macrocyclic alkynones is described. In these reactions, a β-iodoallenolate intermediate is generated via conjugate addition of iodide to an alkynone followed by an intramolecular aldol reaction with a tethered aldehyde to afford a cyclohexenyl alcohol. The Lewis acid magnesium iodide (MgI2) was found to promote irreversible ring closure, while cyclizations using BF3·OEt2 as promoter occurred reversibly...
October 4, 2013: Journal of Organic Chemistry
Ping-Li Lv, Rong-Xiu Zhu, Dong-Ju Zhang, Chong-Gang Duan, Cheng-Bu Liu
The asymmetric epoxidation of 2-cyclohexen-1-one with aqueous H(2)O(2) as oxidant, 1,2-diaminocyclohexane as catalyst, and a Brønsted acid trifluoroacetic acid (TFA) as cocatalyst has been studied by performing density functional theory calculations. It is confirmed that the catalyzed epoxidation proceeds via sequential nucleophilic addition and ring-closure processes involving a ketiminium intermediate. Four possible pathways associated with two Z isomers and two E isomers of ketiminium have been explored in detail...
February 2, 2012: Journal of Physical Chemistry. A
Israel Fernández, Fernando P Cossío, Miguel A Sierra
The seminal report by Hegedus in 1982, showing that alkoxychromium(0) carbenes reacted with imines under bright Colorado sunlight to yield β-lactams, marked the beginning of a key reaction in organometallic chemistry. Very little was known about the mechanism of this reaction. In fact, Hegedus proposed the reversible generation of a chromium-coordinated ketene, which would react with nucleophiles. This coordinated species would show all the advantages of ketenes without their shortcomings, namely, dimerization, formation of undesired adducts, and so forth...
July 19, 2011: Accounts of Chemical Research
Lili Zhao, Xiang Yu Chen, Song Ye, Zhi-Xiang Wang
It has been experimentally reported that PMe(3) catalyzes the cycloalkylation of the pendant halogenated α,β-unsaturated ketones (e.g., 1) at the C(α) position, whereas NHC catalyzes the cycloalkylation of the pendant halogenated α,β-unsaturated esters (e.g., 2) at the C(β) position. A DFT study has been performed to understand the detailed reaction mechanisms and the causes for the different ring closure positions in the two cycloalkylations promoted by the similar catalysts. Both reactions undergo three stages that include the nucleophilic addition of the catalysts (PMe(3) or NHC) to the substrates (1 or 2) and subsequent ring closure via S(N)2 mechanism, the H-elimination by the bases (KOH or K(3)PO(4)), and the catalyst release giving the final products...
April 15, 2011: Journal of Organic Chemistry
Matyas Tursky, Linda L R Lorentz-Petersen, Lasse B Olsen, Robert Madsen
A straightforward and atom-economical method is described for the synthesis of 2,3-disubstituted indoles. Anilines and 1,2-diols are condensed under neat conditions with catalytic amounts of either [Cp*IrCl(2)](2)/MsOH or RuCl(3)·xH(2)O/phosphine (phosphine = PPh(3) or xantphos). The reaction does not require any stoichiometric additives and only produces water and dihydrogen as byproducts. Anilines containing methyl, methoxy, chloro and fluoro substituents can participate in the cyclocondensation. Meta-substituted anilines give good regioselectivity for 6-substituted indoles, while unsymmetrical diols afford excellent regioselectivity for the indole isomer with an aryl or large alkyl group in the 2-position...
December 21, 2010: Organic & Biomolecular Chemistry
Samantha L Riches, Chandreyee Saha, Noelia Fontán Filgueira, Emma Grange, Eoghan M McGarrigle, Varinder K Aggarwal
In this paper, we describe studies on the cyclopropanation of Michael acceptors with chiral sulfur ylides. It had previously been found that semi-stabilized sulfonium ylides (e.g., Ph-stabilized) reacted with cyclic and acyclic enones and substituted acrylates with high ee and that stabilized sulfonium ylides (e.g., ester-stabilized) reacted with cyclic enones again with high ee. The current study has focused on the reactions of stabilized sulfonium ylides with acyclic enones which unexpectedly gave low ee...
June 9, 2010: Journal of the American Chemical Society
Aleem Gangjee, Jie Yang, Sherry F Queener
Six novel C9-methyl-5-substituted-2,4-diaminopyrrolo[2,3-d]pyrimidines 18-23 were synthesized as potential inhibitors of dihydrofolate reductase (DHFR) and as anti-opportunistic agents. These compounds represent the only examples of 9-methyl substitution in the carbon-carbon bridge of 2,4-diaminopyrrolo[2,3-d]pyrimidines. The analogs 18-23 were synthesized in a concise eight-step procedure starting from the appropriate commercially available aromatic methyl ketones. The key step involved a Michael addition reaction of 2,4,6-triaminopyrimidine to the appropriate 1-nitroalkene, followed by ring closure of the nitro adducts via a Nef reaction...
December 15, 2006: Bioorganic & Medicinal Chemistry
Maud Reiter, Hazel Turner, Véronique Gouverneur
Structurally diverse beta-hydroxyenones are shown to undergo nonoxidative 6-endo-trig ring closure to form highly substituted tetrahydropyranones. Amberlyst-15, Al(ClO(4))(3) x 9 H(2)O and [Pd(MeCN)(4)](BF(4))(2) were found to be suitable catalysts for these intramolecular conjugate additions, preventing side reactions, such as dehydration or retroaldolisation. The use of [Pd(MeCN)(4)](BF(4))(2) is particularly effective, as this palladium-mediated reaction is under kinetic control and generates tri- and tetrasubstituted tetrahydropyranones with high levels of diastereocontrol...
September 18, 2006: Chemistry: a European Journal
Lei Jiao, Yong Liang, Jiaxi Xu
The relative (cis, trans) stereoselectivity of the beta-lactam formation is one of the critical issues in the Staudinger reaction. Although many attempts have been made to explain and to predict the stereochemical outcomes, the origin of the stereoselectivity remains obscure. We are proposing a model that explains the relative stereoselectivity based on a kinetic analysis of the cis/trans ratios of reaction products. The results were derived from detailed Hammett analyses. Cyclic imines were employed to investigate the electronic effect of the ketene substituents, and it was found that the stereoselectivity could not be simply attributed to the torquoelectronic model...
May 10, 2006: Journal of the American Chemical Society
Jeffrey T Kuethe, Daniel L Comins
The asymmetric total synthesis of natural (+)-cannabisativine 1 was completed in 19 steps and 7% overall yield. The key synthetic intermediate 29 was prepared with a high degree of stereocontrol in 12 steps starting from chiral 1-acylpyridinium salt 10. Addition of zinc enolate 11 to pyridinium salt 10 furnished dihydropyridone 12 containing two contiguous stereocenters of the correct absolute configuration. Luche reduction of ketone 16 afforded diol 17 in high yield (96%) and excellent diastereoselectivity...
August 6, 2004: Journal of Organic Chemistry
Ian W Davies, Jean-François Marcoux, Jeffery T Kuethe, Michael D Lankshear, Jeremy D O Taylor, Nancy Tsou, Peter G Dormer, David L Hughes, K N Houk, Vildan Guner
Tri- and tetrasubstituted anilines are formed in good to excellent yields by the addition of ketones to vinamidinium salts (up to 98%). The reaction proceeds via the formation of dienone intermediates, which react to form an enamine with the liberated amine. In the case of a nitro, or dimethylaminomethylene substituent, the enamines undergo a facile electrocyclic ring closure to form a cyclohexadiene, which goes on to form anilines with a high degree of selectivity (up to 50:1) with a minor competing pathway proceeding via the enol providing phenols...
February 20, 2004: Journal of Organic Chemistry
Sam P de Visser, Sason Shaik
Benzene hydroxylation is a fundamental process in chemical catalysis. In nature, this reaction is catalyzed by the enzyme cytochrome P450 via oxygen transfer in a still debated mechanism of considerable complexity. The paper uses hybrid density functional calculations to elucidate the mechanisms by which benzene is converted to phenol, benzene oxide, and ketone, by the active species of the enzyme, the high-valent iron-oxo porphyrin species. The effects of the protein polarity and hydrogen-bonding donation to the active species are mimicked, as before (Ogliaro, F...
June 18, 2003: Journal of the American Chemical Society
David R Williams, Richard W Heidebrecht
The first total synthesis of the marine dolabellane diterpene (+)-4,5-deoxyneodolabelline (1) has been accomplished. The highly efficient approach is characterized by the convergent assembly of dihydropyrans 2ab and cyclopentylsilanes 3ab. Allylic silane 3a was prepared from 2-methyl-2-cyclopentenone via a copper-catalyzed 1,4-addition followed by diastereoselective alkylation of the resulting enolate. A chemical resolution of racemic cyclopentanone 8 was effected by (S)-CBS-catalyzed borohydride reduction...
February 19, 2003: Journal of the American Chemical Society
Leo A Paquette, In Ho Kim, Nicolas Cunière
[reaction: see text] A zirconocene-mediated ring contraction of 4-vinylfuranosides generated either from d-arabinose or d-glucose is followed by sequential oxidation to the ketone and alkynyl Grignard addition. The resulting cis-cyclobutanediols are subjected in turn to thermal rearrangement and intramolecular oxymercuration-demercuration. The regiochemistry of the final ring closure is controlled by the nature of R.
January 23, 2003: Organic Letters
Huawu Shao, Zerong Wang, Edith Lacroix, Shih-Hsiung Wu, Harold J Jennings, Wei Zou
2'-Aldehydes and 2'-ketones of alpha-C-glycosides, including the gluco-, galacto-, and manno- series, were epimerized exclusively to their beta-anomers in good-to-excellent yields under basic conditions and in the presence of zinc acetate. The beta-stereoselectivity is independent of the neighboring group at 2-O-substitution of sugar substrates. Therefore, this provides a particularly useful method for the preparation of manno-beta-C-glycosides. The epimerization is likely initiated by the formation of Zn-enolate that is stabilized by intramolecular chelation to the pyranose ring-oxygen to form a syn chair-boat structure...
March 13, 2002: Journal of the American Chemical Society
S M Ludeman, V L Boyd, J B Regan, K A Gallo, G Zon, K Ishii
Phenyl ketone phosphorodiamidates [C6H5C(O)CH2CH2OP(O)NHR1NR2R3] were synthesized in conjunction with an ongoing investigation into the effects of substituents on the dynamical solution chemistry of the metabolites of cyclophosphamide (1a). In contrast to aldophosphamide (3a), which readily interconverts with its cyclic isomer 4-hydroxycyclophosphamide (2a), phenylketophosphamide (14a: R1 = H, R2 = R3 = CH2CH2Cl) exhibited an apparent "resistance" toward an intramolecular addition reaction such that 4-hydroxy-4-phenylcyclophosphamide (13a) could not be detected either spectroscopically (31P or 13C NMR) or chemically (NaCN trapping experiment)...
May 1986: Journal of Medicinal Chemistry
L D Wise, D E Butler, H A DeWald, D M Lustgarten, I C Pattison, D N Schweiss, L L Coughenour, D A Downs, T G Heffner, T A Pugsley
2-(Diethylamino)-N-[4-(2-fluorobenzoyl)-1,3-dimethyl-1H-pyrazol-5-yl] acetamide (1) was recently found to have an antipsychotic-like profile in behavioral animal tests but, unlike clinically available antipsychotic agents, did not interact with dopamine receptors. Compound 1 was apparently metabolized to (5-amino-1,3-dimethyl-1H-pyrazol-4-yl)(2-fluorophenyl)methanone (2), which was both active in the behavioral animal tests and toxic. The synthesis and pharmacological evaluation of a series of 1,3-dialkyl-4-(iminoarylmethyl)-1H-pyrazol-5-ols are described in which the hydroxy and imine functionalities were selected as possible isosteric replacements for the amino and ketone groups of the earlier series...
October 1987: Journal of Medicinal Chemistry
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