- Carbene-catalyzed desymmetrization of 1,3-diols: Access to optically enriched tertiary alkyl chlorides
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The introduction of a chlorine atom to a carbon center in an enantioselective manner via conventional C-Cl bond formation is difficult. Here we report a new approach to this class of tertiary alkyl chlorides with high optical purities. Instead of forming a new C-Cl bond, our approach involves carbene-catalyzed desymmetrization of 2-chloro-1,3-diols as the key step to set up the chiral carbon center with excellent enantiomeric excess.
- Li, Bao-Sheng,Wang, Yuhuang,Proctor, Rupert S. J.,Jin, Zhichao,Chi, Yonggui Robin
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supporting information
p. 8313 - 8316
(2016/07/06)
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- Copper-free arylation of 3,3-disubstituted allylic halides with triazene-softened aryl Grignard reagents
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A copper-free allylic arylation reaction between 3,3-disubstituted allylic halides and triazene-softened aryl Grignard reagents has been developed. This protocol presents a direct and efficient way to construct both α- or γ-isomers with high regioselectivity under environmentally benign conditions. Various functional groups can be tolerated in the reaction and the products are of high value for multiple synthetic applications. The α- and γ-isomers can be converted to the corresponding 3H-indole and indole derivatives in multigram scale respectively.
- Xu, Lijun,Liu, Zhubo,Dong, Weipeng,Song, Jinyu,Miao, Maozhong,Xu, Jianfeng,Ren, Hongjun
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supporting information
p. 6333 - 6337
(2015/06/08)
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- Ruthenium-catalyzed oxidation of allyl alcohols with intermolecular hydrogen transfer: Synthesis of α,β-unsaturated carbonyl compounds
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Ruthenium-catalyzed oxidation of multisubstituted allyl alcohols in the presence of benzaldehyde gives enals or enones in good yields. Unlike the commonly reported ruthenium-catalyzed isomerization reaction of allyl alcohols to give saturated ketones, an intermolecular rather than intramolecular hydrogen transfer is involved in this transformation. This reaction offers an efficient, mild, and high-yielding method for the preparation of substituted α,β-unsaturated compounds.
- Ren, Kai,Hu, Bei,Zhao, Mengmeng,Tu, Yahui,Xie, Xiaomin,Zhang, Zhaoguo
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p. 2170 - 2177
(2014/04/03)
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- Iridium-catalyzed asymmetric hydrogenation of 3,3-disubstituted allylic alcohols in ethereal solvents
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Ir-phosphinomethyl-oxazoline complexes have been identified as efficient, highly enantioselective catalysts for the asymmetric hydrogenation of 3,3-disubstituted allylic alcohols and related homoallylic alcohols. In contrast to other N,P ligand complexes, which require weakly coordinating solvents, such as dichloromethane, these catalysts perform well in more ecofriendly THF or 2-MeTHF. Their synthetic potential was demonstrated with the formal total synthesis of four bisabolane sesquiterpenes. Particularly high enantioselectivity values in the asymmetric hydrogenation of 3,3-disubstituted allylic alcohols and related homoallylic alcohols have been achieved with Ir-phosphinomethyloxazoline catalysts. In contrast to other N,P-ligand complexes, which require weakly coordinating solvents, such as CH 2Cl2, these catalysts perform well in more ecofriendly THF or 2-MeTHF (see scheme; CODa =a 1,5-cyclooctadiene). Copyright
- Bernasconi, Maurizio,Ramella, Vincenzo,Tosatti, Paolo,Pfaltz, Andreas
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supporting information
p. 2440 - 2444
(2014/03/21)
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- Highly enantioselective asymmetric hydrogenation of (E)-β,β- disubstituted α,β-unsaturated Weinreb amides catalyzed by Ir(i) complexes of SpinPhox ligands
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The Ir(i) complexes of chiral spiro phosphino-oxazoline ligands (SpinPhox) have demonstrated good to excellent enantioselectivity in the asymmetric hydrogenation (AH) of a variety of (E)-β,β-disubstituted α,β-unsaturated N-methoxy-N-methylamides, affording the corresponding optically active Weinreb amides with up to 97% ee.
- Shang, Jian,Han, Zhaobin,Li, Yang,Wang, Zheng,Ding, Kuiling
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supporting information; experimental part
p. 5172 - 5174
(2012/06/18)
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- Highly enantioselective asymmetric isomerization of primary allylic alcohols with an iridium-N,P complex
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Access to chiral aldehydes: The asymmetric isomerization of primary allylic alcohols was studied with a bicyclic phosphine-oxazoline iridium catalyst. This method displays a broad substrate scope and leads to the desired chiral aldehydes with excellent enantioselectivities (see scheme; R1, R 2=Ar or alkyl). Copyright
- Li, Jia-Qi,Peters, Byron,Andersson, Pher G.
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supporting information; experimental part
p. 11143 - 11145
(2011/10/31)
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- Improved catalysts for the iridium-catalyzed asymmetric isomerization of primary allylic alcohols based on charton analysis
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An improved generation of chiral cationic iridium catalysts for the asymmetric isomerization of primary allylic alcohols is disclosed. The design of these air-stable complexes relied on the preliminary mechanistic information available, and on Charton analyses using two preceding generations of iridium catalysts developed for this highly challenging transformation. Sterically unbiased chiral aldehydes that were not accessible previously have been obtained with high levels of enantioselectivity, thus validating the initial hypothesis regarding the selected ligand-design elements. A rationale for the high enantioselectivities achieved in most cases is also presented. Achieving enantioselectivity: An improved generation of chiral cationic iridium catalysts for the asymmetric isomerization of primary allylic alcohols is disclosed. The design of these air-stable complexes relies on preliminary mechanistic information and on Charton analyses using two preceding generations of iridium catalysts developed for this highly challenging transformation (see figure).
- Mantilli, Luca,Gerard, David,Torche, Sonya,Besnard, Celine,Mazet, Clement
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supporting information; experimental part
p. 12736 - 12745
(2011/02/21)
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- Catalytic asymmetric formation of δ-Lactones from Unsaturated acyl halides
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Previously unexplored enantiopure zwitterionic ammonium dienolates have been utilized in this work as reactive intermediates that act as diene components in hetero-Diels-Alder reactions (HDAs) with aldehydes to produce optically active δ-lactones, subunits of numerous bioactive products. The dienolates were generated in situ from E/Z mixtures of a,b- unsaturated acid chlorides by use of a nucleophilic quinidine derivative and Sn (OTf)2 as co-catalyst. The latter component was not directly involved in the cycloaddition step with aldehydes and simply facilitated the formation of the reactive dienolate species. The scope of the cycloaddition was considerably improved by use of a complex formed from Er- (OTf)3 and a simple commercially available norephedrine-derived ligand that tolerated a broad range of aromatic and heteroaromatic aldehydes for a cooperative bifunctional Lewis-acid-/ Lewis-base-catalyzed reaction, providing a,b-unsaturated d-lactones with excellent enantioselectivities. Mechanistic studies confirmed the formation of the dienolate intermediates for both catalytic systems. The active ErIII complex is most likely a monomeric species. Interestingly, all lanthanides can catalyze the title reaction, but the efficiency in terms of yield and enantioselectivity depends directly on the radius of the Ln III ion. Similarly, use of the pseudolanthanides ScIII and YIII also resulted in product formation, whereas the larger La III and other transition metal salts, as well as main group metal salts, proved to be inefficient. In addition, various synthetic transformations of 6- CCl3- or 4-silyl-substituted α,β-unsaturated d-lactones, giving access to a number of valuable δ-lactone building blocks, were investigated.
- Tiseni, Paolo S.,Peters, Rene
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supporting information; experimental part
p. 2503 - 2517
(2010/09/03)
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- Iridium-catalyzed asymmetric isomerization of primary allylic alcohols
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Nothing to sm(Ir)k at: Under appropriate reaction conditions, iridium hydride catalysts promote the isomerization of primary allylic alcohols. The best catalysts, like (R)-1 (P green, O red, N blue, Ir yellow), deliver the desired chiral aldehydes with excellent enantioselectivity and good yields. Mechanistic hypotheses have been developed on the basis of preliminary investigations.
- Mantilli, Luca,Gerard, David,Torche, Sonya,Besnard, Celine,Mazet, Clement
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supporting information; experimental part
p. 5143 - 5147
(2009/12/07)
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- Lewis acid-catalyzed Meyer-Schuster reactions: methodology for the olefination of aldehydes and ketones
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In principle, the most efficient and atom-economical means of converting an aldehyde or ketone into the homologated α,β-unsaturated ester is through addition/rearrangement sequences involving acetylenic π-bonds (Scheme 1). Implementation of such a strategy for the synthesis of α,β-unsaturated esters is presented: addition of ethoxyacetylene followed by scandium(III) triflate-catalyzed Meyer-Schuster rearrangement reaction. Stereoselectivities range from good to excellent in the formation of disubstituted α,β-unsaturated esters from aldehydes (Table 3). The two-stage olefination of even the most hindered ketones proceeds with near perfect efficiency (Table 4).
- Engel, Douglas A.,Lopez, Susana S.,Dudley, Gregory B.
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p. 6988 - 6996
(2008/09/21)
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- Olefination of ketones using a gold(III)-catalyzed Meyer-Schuster rearrangement
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An atom-economical and efficient olefination strategy for ketones is described. Ethoxyacetylide addition followed by a gold-catalyzed Meyer-Schuster rearrangement affords α,β-unsaturated esters, generally in excellent overall yield from the starting ketones. The alkynophilicity of Au3+ promotes an interaction with the electron-rich acetylenes that catalyzes the Meyer-Schuster rearrangement selectively over other conceivable pathways.
- Engel, Douglas A.,Dudley, Gregory B.
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p. 4027 - 4029
(2007/10/03)
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- Co-catalyzed reductive cyclization of azido and cyano substituted α,β-unsaturated esters with NaBH4: enantioselective synthesis of (R)-baclofen and (R)-rolipram
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Sodium borohydride in combination with a catalytic amount of CoCl2 has been found to be an excellent catalytic system in reductive cyclizations of suitably substituted azido and cyano groups of α,β-unsaturated esters to afford γ and δ-lactams in high yields. The process has been demonstrated for the enantioselective synthesis of (R)-baclofen, (R)-rolipram, and (R)-4-fluorophenylpiperidinone, a key intermediate for (-)-paroxetine.
- Paraskar, Abhimanyu S.,Sudalai, Arumugam
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p. 4907 - 4916
(2007/10/03)
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- Diastereoselectivity of enolate anion protonation. H/D exchange of β-substituted ethyl butanoates in ethanol-d
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The stereochemistry of base-catalyzed H/D exchange on 13 β-substituted ethyl butanoates in ethanol-d has been studied in order to analyze the steric and electronic factors which control the diastereoselectivity of electrophilic attack on enolate anions. E
- Mohrig, Jerry R.,Rosenberg, Robert E.,Apostol, John W.,Bastienaansen, Mark,Evans, Jordan W.,Franklin, Sonya J.,Frisbie, C. Daniel,Fu, Sabrina S.,Hamm, Michelle L.,Hirose, Christopher B.,Hunstad, David A.,James, Thomas L.,King, Randall W.,Larson, Christopher J.,Latham, Hallie A.,Owen, David A.,Stein, Karin A.,Warnet, Ronald
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p. 479 - 486
(2007/10/03)
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- A New Synthesis of α,β-Unsaturated Carboxylic Esters Using Dialkyltelluronium Carbethoxymethylide
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Dialkyltelluronium carbethoxymethylide was found to condense with a variety of carbonyl compounds to yield α,β-unsaturated carboxylic esters in good yields.
- Osuka, Atsuhiro,Mori, Yasuo,Shimizu, Hirohito,Suzuki, Hitomi
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p. 2599 - 2602
(2007/10/02)
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