- Tuning the Reactivity of Functionalized Diallylic Alcohols: Br?nsted versus Lewis Acid Catalysis
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The chemodivergent reactivity of bifunctional, enol thioether-containing diallylic alcohols in acidic medium is disclosed, highlighting the difference between strong Lewis acid and mild Br?nsted acid catalysis. In the presence of bismuth(III) triflate, allylic alcohol activation affords diversely substituted cyclopentenones in a Nazarov-type electrocyclization, whereas activation of the thioenol ether by p-toluenesulfonic acid provides an entry to α-sulfenylated β,γ-unsaturated ketones. Both methods represent a facile access to the corresponding products under mild conditions, using inexpensive and non-toxic catalytic systems.
- Lempenauer, Luisa,Du?ach, Elisabet,Lemière, Gilles
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supporting information
p. 10285 - 10288
(2017/08/07)
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- Stereospecific Decarboxylative Nazarov Cyclization Mediated by Carbon Dioxide for the Preparation of Highly Substituted 2-Cyclopentenones
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Highly substituted 2-cyclopentenones were stereospecifically and regioselectively constructed with high catalytic efficiency through Lewis-acid catalyzed decarboxylative Nazarov cyclization of the cyclic carbonate derivative, which is prepared by reacting the propargyl alcohol with carbon dioxide in the presence of a silver catalyst. The stereochemistry of the 2-cyclopentenone is strictly controlled by the geometry of the alkene in the starting material. This method is applicable for various substrates.
- Komatsuki, Keiichi,Sadamitsu, Yuta,Sekine, Kohei,Saito, Kodai,Yamada, Tohru
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supporting information
p. 11594 - 11598
(2017/09/11)
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- Copper-catalyzed borylation of α-alkoxy allenes with bis(pinacolato)diboron: Efficient synthesis of 2-boryl 1,3-butadienes
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Something solid to build on: 2-Boryl 1,3-butadienes with various substitution patterns were formed in good to high yields in a copper-catalyzed borylation of α-alkoxy allenes with bis(pinacolato)diboron (see scheme; Bn=benzyl, pin=pinacolate, L is an N-he
- Semba, Kazuhiko,Fujihara, Tetsuaki,Terao, Jun,Tsuji, Yasushi
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supporting information
p. 12400 - 12403
(2013/12/04)
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- Gold-catalyzed highly regioselective oxidation of C-C triple bonds without acid additives: Propargyl moieties as masked α,β-unsaturated carbonyls
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Gold-catalyzed intermolecular oxidations of internal alkynes have been achieved with high regioselectivities using 8-alkylquinoline N-oxides as oxidants and in the absence of acid additives. Synthetically versatile α,β-unsaturated carbonyls are obtained in good to excellent yields and with excellent E-selectivities. A range of functional groups such as THP, MOMO, N3, OTBS, and N-Boc are tolerated. This reaction allows α,β-unsaturated carbonyls to be masked as propargyl moieties, thus offering a practical solution to compatibility issues with these functional groups likely encountered in syntheses of complex structures.
- Lu, Biao,Li, Chaoqun,Zhang, Liming
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supporting information; experimental part
p. 14070 - 14072
(2011/01/04)
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- Synthesis and electronic properties of regioisomerically pure oxochlorins
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We describe a two-step conversion of C-alkylated zinc chlorins to zinc oxochlorins wherein the keto group is located in the reduced ring (17-position) of the macrocycle. The transformation proceeds by hydroxylation upon exposure to alumina followed by dehydrogenation with DDQ. The reactions are compatible with ethyne, iodo, ester, trimethylsilyl, and pentafluorophenyl groups. A route to a spirohexyl-substituted chlorin/oxochlorin has also been developed. Representative chlorins and oxochlorins were characterized by static and time-resolved absorption spectroscopy and fluorescence spectroscopy, resonance Raman spectroscopy, and electrochemistry. The fluorescence quantum yields of the zinc oxochlorins (φf = 0.030-0.047) or free base (Fb) oxochlorins (φf = 0.13-0.16) are comparable to those of zinc tetraphenylporphyrin (ZnTPP) or free base tetraphenylporphyrin (FbTPP), respectively. The excited-state lifetimes of the zinc oxochlorins (τ = 0.5-0.7 ns) are on average 4-fold lower than that of ZnTPP, and the lifetimes of the Fb oxochlorins (τ = 7.4-8.9 ns) are ~40% shorter than that of FbTPP. Time-resolved absorption spectroscopy of a zinc oxochlorin indicates the yield of intersystem crossing is >70%. Resonance Raman spectroscopy of copper oxochlorins show strong resonance enhancement of the keto group upon Soret excitation but not with Qy-band excitation, which is attributed to the location of the keto group in the reduced ring (rather than in the isocyclic ring as occurs in chlorophylls). The one-electron oxidation potential of the zinc oxochlorins is shifted to more positive potentials by approximately 240 mV compared with that of the zinc chlorin. Collectively, the fluorescence yields, excited-state lifetimes, oxidation potentials, and various spectral characteristics of the chlorin and oxochlorin building blocks provide the foundation for studies of photochemical processes in larger architectures based on these chromophores.
- Taniguchi, Masahiko,Holten, Dewey,Lindsey, Jonathan S.,Kim, Han-Je,Ra, Doyoung,Schwartz, Jennifer K.,Kirmaier, Christine,Hindin, Eve,Diers, James R.,Prathapan, Sreedharan,Bocian, David F.
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p. 7329 - 7342
(2007/10/03)
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- Meerwein-Ponndorf-Verley-type reductive acetylation of carbonyl compounds to acetates by lanthanide complexes in the presence of isopropenyl acetate
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Meerwein-Ponndorf-Verley-type reductive acetylation of carbonyl compounds to acetates was successfully carried out in the presence of isopropenyl acetate under the influence of a catalytic amount of Ln(O(i)Pr)3 at room temperature. Various carbonyl compounds were converted into the corresponding acetates in fair to good yields. (C) 2000 Elsevier Science Ltd.
- Nakano, Yasushi,Sakaguchi, Satoshi,Ishii, Yasutaka
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p. 1565 - 1569
(2007/10/03)
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- Highly Regio- and Diastereoselective One-Pot Synthesis of Silyl Epoxy Alcohols and Vinylsilanes by Direct Hydroxy-Epoxidation
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A direct synthesis of silyl epoxy alcohols from vinylsilanes is described.It consists of the regioselective ene reaction of the vinylsilanes with singlet oxygen, which proceeds with predominant hydrogen abstraction at the position geminal to the silyl group.The resulting silyl allylic hydroperoxides were treated, without isolation, subsequently with Ti(O-i-Pr)4 to afford the silyl epoxy alcohols in good yields and very high diastereomeric ratios, which ranged from 93:7 to greater than 97:3.Alternatively, the vinylsilanes were photooxygenated directly in the presence of the titanium catalyst and the silyl epoxy alcohols obtained in good yields.The method was applied to di- and trisubstituted acyclic vinylsilanes with a methyl group geminal to silicon and cyclic derivatives all give consistently good results.In this novel hydroxy-epoxidation, the regioselectivity of the singlet oxygen ene reaction as well as the diastereoselectivity of the oxygen transfer can be controlled by the steering effects of the silyl group.
- Adam, Waldemar,Richter, Markus J.
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p. 3341 - 3346
(2007/10/02)
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- Synthesis and Antimalarial Properties of 1-Imino Derivatives of 7-Chloro-3-substituted-3,4-dihydro-1,9(2H,10H)-acridinediones and Related Structures
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To improve upon the activity and properties of the 3-aryl-7-chloro-3,4-dihydro-1,9(2H,10H)-acridinediones, a variety of 1-imino derivatives (3) were prepared and shown to be highly active antimalarial agents in both rodents and primates.Among structural modifications prepared, including N10-alkyl and C2-substituted analogs, removal of the C9 oxygen, and introduction of an imino side chain at C9, the imines of the N10-H acridinediones were the most active compounds obtained.The imino derivative of7-chloro-3-(2,4-dichlorophenyl)-3,4-dihydro-1,9(2H,10H)-acridinedione (9aa) proved to be highly active in advanced studies in primates.
- Kesten, Stephen J.,Degnan, Margaret J.,Hung, Jocelyn,McNamara, Dennis J.,Ortwine, Daniel F.,et al.
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p. 3429 - 3447
(2007/10/02)
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- Efficient Transformation of Methyl Propargyl Ethers into α,β-Unsaturated Ketones
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Methyl propargyl ethers, obtained from carbonyl compounds by successive treatment with an acetylide and MeI, were easily converted to the corresponding α,β-unsaturated ketone by regioselective hydration of acetylenic moiety followed by elimination of methanol under the catalytic action of Au(III).
- Fukuda, Yukitoshi,Utimoto, Kiitiro
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p. 2013 - 2015
(2007/10/02)
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- A FACILE, STEREOSELECTIVE PREPARATION OF (Z)-2,4-PENTADIENOATES BY FAVORSKII REARRANGEMENT
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Reaction of 1,3,4-tribromo-2-alkanones, efficiently prepared by direct bromination of the parent enone, with methanolic sodium methoxide gives methyl (Z)-2,4-pentadienoates with high (Z) selectivity about the α,β-double bond.
- Engler, Thomas A.,Falter, Wolfgang
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p. 4115 - 4118
(2007/10/02)
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- Acetylation de trimethylsilyl bicyclo(n,1,0)alcanes : nouvelles syntheses de l'acetyl cyclohexene-2 et d'acetyl bicyclo(n,1,0)alcanes
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Acetylation of trimethylsilyl bicyclo(n,1,0)alkanes was studied using the CH3COCl/AlCl3 complex.The results showed that both larger cycle size (n = 3, 4 or 6) and stereochemistry of the substrate (SiMe3 group in endo or exo position) played a prominent role in the orientation of the reaction : depending upon the starting products, either bicyclic or ethylenic and/or chloro ketones were formed.The results can be rationalized in terms of steric hindrance considerations.They allowed us to propose a new convenient synthesis of acetyl bicyclo(n,1,0)alkanes and also of 1-acetyl 2-cyclohexene.
- Ahra, M.,Grignon-Dubois, M.
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p. 820 - 824
(2007/10/02)
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- GEM-DISILYLCYCLOPROPANES: PREPARATION ET UTILISATION EN SYNTHESE ORGANIQUE
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A simple general route for the conversion of olefins to gem-disilylcyclopropanes, involving the dichlorocyclopropanation of the double bond followed by silylation using the Me3SiCl/Li/THF reagent at 0-10 deg C, is described.Acetylation of bicyclic derivatives thus obtained constitutes an original synthesis of cycloalkylidene ketones by a process more convenient than those previously used, and also provides new acetyl dihydrofurans.
- Laguerre, Michel,Grignon-Dubois, Micheline,Dunogues, Jacques
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p. 1161 - 1169
(2007/10/02)
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