- A novel cyclization reaction of a C-6 substituted uridine analog: An entry to 5,6-dialkylated uridine derivatives
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5,6-Dialkylated uridine derivatives were conveniently synthesized in 5 steps starting from 2',3'-O-isopropylideneuridine (1) in a 43% overall yield. The key reaction is a novel acid catalyzed cyclization reaction of 6-(4-butanal)-2',3'-O-isopropylideneuridine.
- Wang,Kagel,Rao,Mertes
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- Formation of carbocycles by intramolecular conjugate displacement: Scopeand mechanistic insights
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A detailed study has been made of a method of ring closure categorized as an all-carbon intramolecular conjugate displacement (ICD). This reaction involves intramolecular addition of a carbanion, which is stabilized by at least one electron-withdrawing group, to a Michael acceptor which has a leaving group in an allylic position. The process formally resembles a combination of Michael addition and S N2' displacement. The overall result is formation of a ring with loss of the allylic leaving group and shift of the original double bond to a new location spanning the positions of the electron-withdrawing substituent of the Michael acceptor subunit and the original allylic leaving group. The starting materials are easily prepared by a selenium-based version of the Morita-Baylis-Hillman reaction. The cyclizations are transition metal free and occur under mild conditions, using DBU or Cs 2CO 3 inMeCN or THF. Acetate is a suitable leaving group and the electron-withd rawing substituent of the Michael acceptor unit can be CO 2R,SO 2Ph, or CN. Six- and seven-membered rings are formed effi ciently, and complex structures, such as those resembling the core of CP-225,917, are easily assembled. The products of these ICD reactions are themselves classical Michael acceptors. A range of mechanisms probably operates, depending on the structure of the starting material and the reaction conditions, but conclusive evidence for a stepwise mechanism was obtained in a suitably biased case, while other observations are compatible with a concerted process or a stepwise path involving a short-lived carbanion that evades capture by a proton source.
- Wang, Lihong,Prabhudas, Bodhuri,Clive, Derrick L. J.
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supporting information; experimental part
p. 6003 - 6012
(2009/09/25)
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- Iron(III) tosylate in the preparation of dimethyl and diethyl acetals from ketones and β-keto enol ethers from cyclic β-diketones
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An efficient method for conversion of ketones to their corresponding dimethyl and diethyl acetals and of cyclic β-diketones into β-keto enol ethers using Fe(OTs)3 as a catalyst is described. Copyright Taylor & Francis Group, LLC.
- Mansilla, Horacio,Afonso, Maria M.
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p. 2607 - 2618
(2008/12/22)
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- Process for preparing derivatives of 4-halobutyraldehyde
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The present invention describes a process for preparing an enol ester of a 4-halo-butyraldehyde which comprises contacting a cyclopropane carboxaldehyde (CPCA) and a carboxylic acid halide in the presence of a Lewis acid catalyst. In addition, the present invention relates to a process for preparing an acetal of a 4-halo-butyraldehyde which comprises contacting an enol ester of a 4-halo-butyraldehyde, prepared according to the present invention, with an alcohol in the presence of a certain acid catalyst.
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- Vinylcyclobutanols: A composite functional group?
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The effect of small strained rings on chemical reactivity was probed by the examination of the behavior of vinylcyclobutanols as terminators in cyclization reactions. The substrates were readily available by the addition of vinyllithium reagents bearing acetals as cyclization initiators to cyclobutanone. Bronsted and Lewis acids both promoted cyclization in contrast to vinylcyclopropanol terminators for which Bronsted acids failed. The products are spirocycles consisting of a cyclopentanone derived from ring expansion of the cyclobutanol and the second ring derived by attack of the terminator on the initiator. Spirocyclization to [4.5] and [4.6] systems proceeded smoothly, whereas spirocyclization to a [4.7] system failed. Attaching the cyclization termini to a preexisting ring system (whereby tricycles consisting of a fused bicycle and a spirocycle are formed) expands the scope of the cyclization to include the [4.7] ring system even at 0.01 M, a rather high concentration for such an unfavorable ring system. The diastereoselectivity generally placed the initiator substituent and the carbon-carbonyl bond of the cyclopentanone ring trans on the newly formed ring. Cyclic acetals and the free aldehyde also served as initiators. The mechanistic implications of these observations are discussed.
- Trost, Barry M.,Chen, Deborah W. C.
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p. 12541 - 12554
(2007/10/03)
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- Regiochemistry of the Intramolecular Photocycloaddition of Enones to Vinyl Ethers as a Function of Chain Length
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The intramolecular cycloaddition of a cyclohexenone moiety bound to a vinyl ether fragment has been explored.The regiochemistry and the quantum yield of the reaction has been investigated as a function of the chain length n and the position of the methoxy group.It has been found that in those cases where the chain consists of three and four members the position of the methoxy group has no influence on the regiochemistry but on the quantum yield.Only head-to-head cycloaddition is observed.In the case of n = 2 both the regiochemistry and the quantum yield depend strongly on the position of the methoxy group.It is concluded that the main reason for the different behavior of n = 2 is due to a through-bond effect between the two olefinic units mediated by a C2H4 bridge. Key Words: Rule of five / Photocycloaddition / Regiochemistry / Enones / Vinyl ethers
- Gleiter, Rolf,Fischer, Evelyn
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p. 1899 - 1912
(2007/10/02)
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- The Acyl Effect on Intramolecular Palladium-Catalyzed Trimethylenemethane Cycloadditions
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Enhancing the generality of the intramolecular palladium-catalyzed cycloaddition involving trimethylenemethane complexes as reactive intermediates is possible by incorporation of acyl substituents on the TMM unit.Such substituted TMM-PdL2 species greatly expand the scope such that bicyclooctyl, bicyclononyl, and bicyclodecyl ring systems all can be created.Furthermore, the acyl-TMM chemistry permits incorporation of a bridgehead methyl substituent - the first example of a TMM-PdL2 cycloaddition in synthetically useful yields initiated byattack of a tertiary carbon in the first step to give a quaternary center.The requisite substrates are readily available using nucleophilic acylations via lithiated thioacetals.A general lynchpin strategy derives from bis(methylthio)methane onto which can be attached both the donor and acceptor partners of the cycloaddition. 2-((Trimethylsilyl)methyl)propenal serves as a convenient conjunctive reagent to introduce the donor partner.Alternatively 2-acyldithianes serve as a lynchpin to build substrates leading to bicycles bearing bridgehead substituents.In this case, 2-bromo-3-(trimethylsilyl)propene serves as a convenient conjunctive reagent to create the donor partner.The beneficial effect of acyl substitution derives from a combination of inhibiting side reactions derived from protodesilylation processes and facilitating the initial step of this nonconcerted cycloaddition.In addition to improving the generality of the intramolecular process, the ketone group that results in the product is a powerful functionality for further structural elaboration.
- Trost, Barry M.,Grese, Timothy A.
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p. 686 - 697
(2007/10/02)
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- Chiral Construction of the Estrane Ring System by an Intramolecular Double Michael Reaction
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Construction of the estrane ring system was achieved by the intramolecular double Michael reaction as the key step.Heating of the α,β-unsaturated enone ester (18), prepared from the optically active indanone (4), with chlorotrimethylsilane, triethylamine, and zinc chloride produced three estrane derivatives (19), (22), and (25).
- Ihara, Masataka,Takahashi, Takako,Shimizu, Noriko,Ishida, Yohhei,Sudow, Izumi,et al.
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p. 529 - 535
(2007/10/02)
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- BIFUNCTIONAL ANNULATING REAGENTS: STUDIES ON THE UTILITY OF NOVEL TIN BASED ANNULATING REAGENTS IN THE PREPARATION OF SIX AND SEVEN MEMBERED RINGS
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The acetal stannanes (2) and (3) have been prepared and shown to be of limited use for the preparation of six and seven-membered rings due to an enhanced ability to undergo an alternative β-elimination reaction.A tentative explanation for this enhancement is presented.
- Lee, Thomas V.,Boucher, Raymond J.,Ellis, Karen L.,Richardson, Kevan A.
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p. 685 - 688
(2007/10/02)
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- Syntheses of homologous omega-aminated 1-methoxyalkyl beta-D-glucopyranosides as potential beta-D-glucosidase inhibitors.
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(R)- and (S)-2-Azido-1-methoxyethyl beta-D-glucopyranosides (16) and (17), (R)- and (S)-3-azido-1-methoxypropyl beta-D-glucopyranosides (18) and (19), (R,S)-4-azido-1-methoxybutyl beta-D-glucopyranoside (20), and (R,S)-5-azido-1-methoxypentyl beta-D-glucopyranoside (22) were synthesized from omega-substituted dimethyl acetals of acetaldehyde, propanal, butanal, and pentanal by trimethylsilyl triflate-catalysed transacetalation using 1-O-trimethysilyl 2,3,4,6-tetra-O-acetyl-beta-D-glucose (1) as acceptor. Most of the acetylated (R,S)-epimers could be resolved into pure compounds by column chromatography. Preliminary tests showed that the deacetylated acetal glucosides carrying omega-bromo, azido, or acetamido substituents in the aglycon are good substrates for beta-D-glucosidase from sweet almonds. The corresponding omega-amino derivatives of compounds 16, 19, 20, and 22, (R)-2-amino-1-methoxyethyl beta-D-glucopyranoside (23), (S)-3-amino-1-methoxypropyl beta-D-glucopyranoside (24), (R,S)-4-amino-1-methoxybutyl beta-D-glucopyranoside (25), and (R,S)-5-amino-1-methoxypentyl beta-D-glucopyranoside (26) proved almost completely resistant to beta-D-glucosidase. The stability of the glucosides against enzyme hydrolysis is dependent on the distance between the amino group and the anomeric center.
- Lehmann,Ziser
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- STEREOCONTROLLED TOTAL SYNTHESIS OF (+/-)-NORPATCHOULENOL AND TWO METABOLITES OF PATCHOULI ALCOHOL, (+/-)-HYDROXY PATCHOULI ALCOHOL AND THE CORRESPONDING (+/-)-CARBOXYLIC ACID
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The first total synthesis of the two biooxidation products of patchouli alcohol (2), (+/-)-hydroxy patchouli alcohol (3) and the corresponding (+/-)-carboxylic acid 4, has been achieved in highly stereocontrolled manners.Synthesis of (+/-)-norpatchoulenol (1), the real odoriferous substance of patchouli oil, has been accomplished by the biogenetic route via (+/-)-3 and (+/-)-4.
- Niwa, Haruki,Hasegawa, Takashi,Ban, Norikazu,Yamada, Kiyoyuki
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p. 825 - 834
(2007/10/02)
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- STEREOCONTROLLED TOTAL SYNTHESIS OF (+/-)-HYDROXY PATCHOULI ALCOHOL AND THE CORRESPONDING (+/-)-CARBOXYLIC ACID, METABOLITES OF PATCHOULI ALCOHOL, AND (+/-)-NORPATCHOULENOL
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The first total synthesis of (+/-)-hydroxy patchouli alcohol (3) and the corresponding (+/-)-carboxylic acid 4, the biooxidation products of patchouli alcohol (2) has been achieved. (+/-)-Norpatchoulenol (1) has also been synthesized by the biogenetic route via 3 and 4.
- Niwa, Haruki,Hasegawa, Takashi,Ban, Norikazu,Yamada, Kiyoyuki
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p. 2797 - 2800
(2007/10/02)
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- Production of unsaturated carbocyclic ketones
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Preparation of α,β-unsaturated carbocyclic ketones by reacting an enol lactone with a carbanion generated by treatment of a methylphosphonate or a mono-substituted methylphosphonate with base.
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