- Enantioselective, Catalytic Multicomponent Synthesis of Homoallylic Amines Enabled by Hydrogen-Bonding and Dispersive Interactions
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We report a one-step catalytic, enantioselective method for the preparation of homoallylic N-Boc amines directly from acetals. Reactive iminium ion intermediates are generated in situ through the combination of an acetal, a chiral thiourea catalyst, trialkylsilyl triflate, and N-Boc carbamate and are subsequently trapped by a variety of allylsilane nucleophiles. No homoallylic ether byproducts are detected, consistent with allylation of the iminium intermediate being highly favored over allylation of the intermediate oxocarbenium ion. Acetals derived from aromatic aldehydes possessing a variety of functional groups and substitution patterns yield homoallylic amines with excellent levels of enantiomeric enrichment. Experimental and computational data are consistent with an anchoring hydrogen-bond interaction between the protioiminium ion and the amide of the catalyst in the enantiodetermining transition state, and with stereodifferentiation achieved through specific noncovalent interactions (NCIs) with the catalyst pyrenyl moiety. Evidence is provided that the key NCI in the major pathway is a π-stacking interaction, contrasting with the cation-πinteractions invoked in previously studied reactions promoted by the same family of aryl-pyrrolidino-H-bond-donor catalysts.
- Ronchi, Elisabetta,Paradine, Shauna M.,Jacobsen, Eric N.
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supporting information
p. 7272 - 7278
(2021/05/26)
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- Formation of Acetals and Ketals from Carbonyl Compounds: A New and Highly Efficient Method Inspired by Cationic Palladium
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The development of a new, highly efficient, and simple method for masking carbonyl groups as acetals and ketals is described. This methodology relies on the nature of the palladium catalyst to direct the acetalization/ketalization reaction. This new protocol is mild and proceed with a very low catalyst loading at ambient temperatures. The method has been extended to a wide variety of different carbonyl compounds with various steric encumbrances to form the corresponding acetals and ketals in excellent yields.
- Green, Shawn D.,Kindoll, Tyler,Lazaro-Martinez, Brenda,Mensah, Enoch A.,West, Jesse
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p. 1810 - 1814
(2019/09/09)
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- A new total synthesis of (±)-α-noscapine
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A new, convergent total synthesis of (±)-α-noscapine was developed on a grams scale through the condensation of 3-trimethylsilyl-meconin derivative 9 and the iodized salt cotarnine derivative 20 as the key step. Staring from simple 2,3-dimethoxybenzoic acid, piperonal and 2,2-dimethoxyethanamine, through the traditional chemical processes to give the final product in 11.6% yield over 14 steps.
- Mao, Yongjun,Song, Shuai,Zhao, Dongmei,Cheng, Maosheng
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p. 2633 - 2640
(2014/01/06)
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- New two-step sequence involving a hetero-Diels-Alder and a nonphenolic oxidative coupling reaction: A convergent access to analogs of steganacin
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A new family of analogs of steganacin, an important antimitotic compound, was accessed. It takes advantage of a completely stereoselective sequence of two key steps. The central dihydropyrane core is built by a highly diastereoselective and facially controlled hetero-Diels-Alder reaction. It is followed by a nonphenolic biaryl oxidative coupling with a complete atropo-stereoselectivity. It leads to a quick way to form cyclic biaryl lignans.
- Laurent, Mathieu Y.,Stocker, Vivien,Temgoua, Valéry Momo,Dujardin, Gilles,Dhal, Robert
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supporting information; experimental part
p. 1608 - 1611
(2011/04/26)
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- Dichotomous reactivity in the reaction of triethyl- and triphenylphosphane HBr salts with dimethyl acetals: A novel entry to α-alkoxy-functionalized ylides and general synthesis of vinyl ethers and alkoxy dienes
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The discovery of dichotomous reactivity in the reaction of trialkyl- vs. triphenylphosphane HBr salts with acetals allows entry to functionalized α-methoxy phosphonium salts and a novel process for tertiary phosphane methylation. The new protocol opens a general entry to the synthesis of vinyl ethers and differentially substituted 1,3-dienes via Wittig reactions of the functionalized ylides derived from the α-methoxy phosphonium salts.
- Das, Priyabrata,McNulty, James
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supporting information; experimental part
p. 3587 - 3591
(2010/09/05)
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- Zinc chloride as an efficient catalyst for chemoselective dimethyl acetalization
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Commercially available anhydrous zinc chloride has been found to be a highly efficient catalyst for dimethyl acetalization in high yields by treatment of aldehydes and ketones with trimethyl orthoformate in methanol-cyclohexane at reflux temperature. Copyright Taylor & Francis Group, LLC.
- Roy, Anupam,Rahman, Matiur,Das, Sudarshan,Kundu, Dhiman,Kundu, Shrishnu Kumar,Majee, Adinath,Hajra, Alakananda
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experimental part
p. 590 - 595
(2009/07/04)
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- Tetrafluoroboric acid adsorbed on silica gel as a reusable heterogeneous dual-purpose catalyst for conversion of aldehydes/ketones into acetals/ketals and back again
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Aldehydes and ketones can be protected as acetals and ketals by treatment with trimethyl orthoformate (TMOF) or triethyl orthoformate (TEOF) under the catalytic influence of tetrafluoroboric acid adsorbed on silica gel (HBF 4-SiO2). In the case of aldehydes or ketones with highly electrophilic carbonyl group, the reactions are carried out under solvent-free conditions. Aryl alkyl ketones, aryl styryl ketones, aldehydes with weakly electrophilic carbonyl groups, and aldehydes with substituents that can coordinate with the catalyst require the presence of the corresponding alcohol as solvent. For substrates that can be converted into acetals under neat conditions, the acetal formation takes place at a faster rate when the alcohol is used as the solvent. The catalyst can be recovered and reused/recycled four times (after reactivation after each use) without any significant decrease in its catalytic efficiency. The parent aldehydes/ketones are regenerated from the corresponding acetals/ketals in high yields by the treatment with water-alcohol in the presence of HBF4-SiO2 at room temperature for short times. Excellent selectivity was observed during inter- and intramolecular competition studies involving carbonyl substrates with varying electronic and steric environments. Selective acetal formation of benzaldehyde takes place in the presence of 4-(dimethylamino)benzaldehyde, thiophene-2-carboxaldehyde, 1-naphthaldehyde, 9-anthraldehyde, or acetophenone, but 3-nitrobenzaldehyde undergoes selective acetal formation in preference to benzaldehyde. In the case of 4-acetylbenzaldehyde, exclusive acetal formation of the aldehyde carbonyl group occurs. Georg Thieme Verlag Stuttgart.
- Kumar, Dinesh,Kumar, Raj,Chakraborti, Asit K.
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p. 1249 - 1256
(2008/12/22)
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- An efficient and versatile procedure for the synthesis of acetals from aldehydes and ketones catalyzed by lithium tetrafluoroborate
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Acetals are obtained in good to excellent yields by treatment of aldehydes and ketones with trialkyl orthoformate and the corresponding alcohol in the presence of a catalytic amount of lithium tetrafluoroborate. Due to the mild reaction conditions, this method is compatible with acid-sensitive substrates.
- Hamada, Nao,Kazahaya, Kiyoshi,Shimizu, Hisashi,Sato, Tsuneo
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p. 1074 - 1076
(2015/10/07)
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- An efficient protection of carbonyls and deprotection of acetals using decaborane
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Carbonyls were efficiently converted to the corresponding dimethyl acetals at room temperature using trimethyl orthoformate and 1 mol% of decaborane under a nitrogen atmosphere. In turn, acetals were deprotected to the corresponding carbonyls using 1 mol% of decaborane in aqueous THF chemoselectively.
- Lee, Seung Hwan,Lee, Ji Hee,Yoon, Cheol Min
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p. 2699 - 2703
(2015/10/07)
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- High Yield Endoselective Heterocycloadditions involving Benzylidenepyruvic Esters as the Heterodiene and an Alkoxystyrene as the Dienophile
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The benzylidenepyruvic esters 6, 10a-d and 11 smoothly reacted with the alkoxystyrenes 12 and 13 in refluxing hexane or toluene and in the presence of catalytic amounts of Eu(fod)3, thus selectively leading to the endo adducts 14-21 in high yields.This represents the first examples of an efficient heterocycloaddition of styrene derivatives without using the high pressure technique.The above adducts are potential intermediates for sugiresinol 7 and related tetrahydropyran neolignans.
- Dujardin, Gilles,Maudet, Mickael,Brown, Eric
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p. 8619 - 8622
(2007/10/02)
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- Influence of Alkoxyalkyl Substituents in the Regioselective Lithiation of the Benzene Ring
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The concomitant presence of an alkoxyalkyl group (α-alkoxyalkyl, α- or β-dialkoxyalkyl) and of an alkoxy group in the relative positions 1 and 3 in a benzene ring generally permits an easy lithiation of position 2 by proton-metal exchange with n-butyllithium; the only aromatic compound tested, bearing a β-alkoxyalkyl group, gave, however, extensive decomposition in the metalation step.Reaction of the metalated species with an electrophile (such as carbon dioxide or ethyl chloroformate) leads to the corresponding substituted products in good to excellent yields.The following transformations are described: 3,4-dimethoxybenzyl α-ethoxyethyl ether (1) into 6,7-dimethoxyphthalide (15); 3,4-(methylenedioxy)benzyl α-ethoxyethyl ether (2) into 6,7-(methylenedioxy)phthalide (16); 3,4-dimethoxybenzyl methyl ether (3) into ethyl 2-(methoxymethyl)-5,6-dimethoxybenzoate (18) and into ethyl 2-(chloromethyl)-5,6-dimethoxybenzoate (20); 3,4-(methylenedioxy)benzyl methyl ether (4) into ethyl 2-(methoxymethyl)-5,6-(methylenedioxy)benzoate (19) and into ethyl 2-(chloromethyl)-5,6-(methylenedioxy)benzoate (21); 3,4-dimethoxybenzaldehyde dimethyl acetal (5) into 5,6-dimethoxyphthalaldehydic acid (22); 3,4-(methylenedioxy)benzaldehyde dimethyl acetal (6) into 5,6-(methylenedioxy)phthalaldehydic acid (23); (3,4-dimethoxyphenyl)acetaldehyde dimethyl acetal (7) into ethyl 2-(2,2-dimethoxyethyl)-5,6-dimethoxybenzoate (25); 3,4,4'-trimethoxydeoxybenzoin ethylene acetal (10) into 2-(ethoxycarbonyl)-3,4,4'-trimethoxydeoxybenzoin (26); 4,3',4'-trimethoxydeoxybenzoin ethylene acetal (11) into 2'-(ethoxycarbonyl)-4,3',4'-trimethoxydeoxybenzoin (27); 3,4,3',4'-tetramethoxydeoxybenzoin ethylene acetal (12) into a mixture of 3-(3,4-dimethoxybenzylidene)-6,7-dimethoxyphthalide (28) and 3-(3,4-dimethoxyphenyl)-7,8-dimethoxyisocoumarin (29).The dioxole ring of methylenedioxy-substituted benzenes is sometimes unstable under these metalation conditions, and partial decomposition usually causes the yields to be lower than those in the case of the corresponding methoxy-substituted benzenes.Many of the products listed above, which have been already prepared by other methods, are more conveniently obtained by the present approach.
- Napolitano, Elio,Giannone, Enrico,Fiaschi, Rita,Marsili, Antonio
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p. 3653 - 3657
(2007/10/02)
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