- Complex Polyheterocycles and the Stereochemical Reassignment of Pileamartine A via Aza-Heck Triggered Aryl C-H Functionalization Cascades
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Structurally complex benzo- and spiro-fused N-polyheterocycles can be accessed via intramolecular Pd(0)-catalyzed alkene 1,2-aminoarylation reactions. The method uses N-(pentafluorobenzoyloxy)carbamates as the initiating motif, and this allows aza-Heck-type alkene amino-palladation in advance of C-H palladation of the aromatic component. The chemistry is showcased in the first total synthesis of the complex alkaloid (+)-pileamartine A, which has resulted in the reassignment of its absolute stereochemistry.
- Bower, John F.,Caiger, Lewis,García-Cárceles, Javier,Hazelden, Ian R.,Jones, Benjamin T.,Langer, Thomas,Lewis, Richard J.
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p. 15593 - 15598
(2021/10/12)
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- Asymmetric Nazarov Cyclizations of Unactivated Dienones by Hydrogen-Bond-Donor/Lewis Acid Co–Catalyzed, Enantioselective Proton-Transfer
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We report an enantioselective Nazarov cyclization catalyzed by chiral hydrogen-bond-donors in concert with silyl Lewis acids. The developed transformation provides access to tri-substituted cyclopentenones in high levels of enantioselectivity (up to 95% e.e.) from a variety of simple unactivated dienones. Kinetic and mechanistic studies are consistent with a reversible 4π-electrocyclization C?C bond-forming step followed by rate- and enantio-determining proton-transfer as the mode of catalysis. (Figure presented.).
- Metternich, Jan B.,Reiterer, Martin,Jacobsen, Eric N.
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supporting information
p. 4092 - 4097
(2020/09/01)
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- Highly enantioselective hydrogenation of 2-substituted-2-alkenols catalysed by a ChenPhos-Rh complex
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Highly enantioselective hydrogenation of a variety of 2-substituted-2- alkenols has been achieved using a ChenPhos-Rh complex as catalyst, giving ≥99% ee for most substrates. Optically active antifungal agent amorolfine was first synthesised using hydrogenation as the key step. This journal is
- Wang, Quanjun,Liu, Xueying,Liu, Xian,Li, Bin,Nie, Huifang,Zhang, Shengyong,Chen, Weiping
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supporting information
p. 978 - 980
(2014/01/06)
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- Divergent regioselectivity in the synthesis of trisubstituted allylic alcohols by nickel- and ruthenium-catalyzed alkyne hydrohydroxymethylation with formaldehyde
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Stoichiometric metals banned: Nonsymmetrically disubstituted alkynes were converted into primary trisubstituted allylic alcohols upon exposure to paraformaldehyde in the presence of nickel or ruthenium catalysts, which exhibit complementary regioselectivity and complete stereoselectivity in the absence of exogenous reducing agents (see scheme). Copyright
- Bausch, Cory C.,Patman, Ryan L.,Breit, Bernhard,Krische, Michael J.
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supporting information; experimental part
p. 5687 - 5690
(2011/08/06)
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- An organocatalytic asymmetric nazarov cyclization
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An organocatalytic asymmetric Nazarov cyclization of diketoesters that proceeds by means of a dual activation mechanism has been developed. Screening of a number of catalysts led to a new thiourea that incorporates a primary amino group. The method gives rise to cyclic products with two adjacent quaternary asymmetric carbon atoms, one of which is an all-carbon stereocenter, with complete or nearly complete diastereoselectivity and in high or very high enantiomeric excess. A brief and very convenient synthesis of the acyclic diketoester starting materials through nucleophilic addition to a ketene is also described.
- Basak, Ashok K.,Shimada, Naoyuki,Bow, William F.,Vicic, David A.,Tius, Marcus A.
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supporting information; experimental part
p. 8266 - 8267
(2010/08/04)
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- Enantioselective synthesis of (2R,4'R,8'R)-α-tocopherol (Vitamin E) based on enzymatic function
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Syntheses of (S)-chroman-2-carboxaldehyde congener 1 and (S)-chiral isoprene unit 3 were achieved based on the enzymatic acetylation of (±)- chroman-2-methanol 6 and (±)-(2,3)-anti-2-methyl-3-(p-methoxyphenyl)-1,3- propane diol 12, respectively. Synthesis of the side-chain part corresponding to (3R,7R)-3,7,11-trimethyldodecan-1-ol 27 was achieved by the coupling reaction of (S)-3 and (R)-3,7-dimethyloctyl iodide 4. The Wittig reaction of (3R,7R)-phosphonium salt 2 derived from (3R,7R)-27 and (S)-1 gave the olefin 28 which was subjected to catalytic hydrogenation to afford (2R,4'R,8'R)-α- tocopherol.
- Nozawa, Masako,Takahashi, Keiko,Kato, Keisuke,Akita, Hiroyuki
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p. 272 - 277
(2007/10/03)
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- Acyclic Stereoselection in the Ortho Ester Claisen Rearrangement
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The ortho ester Claisen rearrangement of trisubstituted allylic alcohols exhibits significant levels of diastereoselection. In E allylic alcohols, a 1,3-diaxial interaction develops in the chairlike transition state leading to the anti isomer, rendering the reaction syn selective by a factor of 3-5 to 1. In Z allylic alcohols, the 1,3-diaxial interaction develops in the transition state leading to the syn isomer, generating an anti:syn selectivity of 6-15 to 1. The relative stereochemistry of the syn isomer was confirmed independently by the synthesis of the mycotoxin botryodiplodin.
- Daub, G. William,Edwards, James P.,Okada, Carol R.,Allen, Jana Westran,Maxey, Claudia Tata,Wells, Matthew S.,Goldstein, Alexandra S.,Dibley, Michael J.,Wang, Clarence J.,Ostercamp, Daniel P.,Chung, Steven,Cunningham, Paula Shanklin,Berliner, Martin A.
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p. 1976 - 1985
(2007/10/03)
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- A Study of Enantioselective Reduction of para-Substituted 2-Methyl-cinnamaldehydes by Baker's Yeast
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Reduction of a series of para-substituted 2-methyl-cinnamaldehydes (1-7) at 20°C and at pH = 2-3 afforded S-enantiomers of saturated alcohols 8-14 in 20-80% yield and 75 - ≥ 99% enantiomeric excess (e.e.); at 30°C, lower yields and e.e.s were obtained. Relative rates of the formation of allylic alcohols 15-21, catalyzed by alcohol dehydrogenase (ADH), correlate with the Hammett σ+ values of para-substituents, revealing that a more efficient delocalization of the positive charge on carbonylic carbon slow down the reduction rates, whereas no correlation of the electronic properties of the substituents with the rate of C=C double bond reduction, catalyzed by enoate reductase, is observed. On reduction of 3 by dried yeast in 2H2O, α,β-carbon atoms in 10a bear 2H atoms, in accordance with the previously reported hydrogenation of selectively 2H-labeled cinnamic aldehyde and cinnamic alcohol. The accumulated data indicate that the mechanism of the enone C=C bond reduction that comprises nucleophilic attack of the hydride ion species on the β-carbon in the first step, followed by enantioselective protonation on the α-carbon atom.
- Sunjic, Vitomir,Majeric, Maja,Hamersak, Zdenko
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p. 643 - 660
(2007/10/03)
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- Synthesis of 3-(4'-Methoxy-1'-phenyl)allyl Citronellyl Ether and Related Structures
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Substituted aromatic allyl citronellyl ethers (1-4) have been prepared and structures supported by spectral data.The compounds were tested for juvenile hormone activity.
- Bhatia, M. S.,Rani, Poonam,Xavierkutty, M. C.,Lal, Jawahar
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p. 411 - 413
(2007/10/02)
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