113304-84-0Relevant articles and documents
Synthesis of the bicyclic core of pumiliotoxins
Sudau, Alexander,Muench, Winfried,Bats, Jan-W.,Nubbemeyer, Udo
, p. 3304 - 3314 (2002)
The bicyclic core of the pumiliotoxins was synthesized in nine to eleven steps starting from L-(-)-proline. This chiral pool starting material was initially converted into an optically active 2-vinylpyrrolidine by standard operations. The first key step allowed the generation of a nine-membered ring lactam by means of a zwitterionic aza-Claisen rearrangement. The 1,4 chirality transfer was found to be low, but the double bond of the azoninone was generated with an exclusive trans configuration in a planar-S arrangement. The mixture of diastereomers thus obtained was immediately epoxidized; the planar chiral information could be completely used to build up new stereogenic centers. Subsequent ring closure under hydrogenolytic conditions resulted in the formation of the bicyclic core with a bridgehead of defined configuration. The hydroxyl group of that material could be protected as a TBS ether, or alternatively a sequence of a Swern oxidation and subsequent methyl Grignard addition gave the complete bicyclic framework with low C8 diastereoselectivity. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
Catalytic epoxidation of unfunctionalized alkenes by dinuclear nickel(II) complexes
Rispens, Minze T.,Gelling, Onko Jan,De Vries, Andre H.M.,Meetsma, Auke,Van Bolhuis, Fre,Feringa, Ben L.
, p. 3521 - 3546 (1996)
The synthesis, crystal and molecular structure and catalytic activity in epoxidation reactions of new dinuclear nickel(II)-complexes, octahedral μ-diacetato-μ-[2,6-bis[N-2-2'-pyridylethyl)formimidoyl]phenolato]bis nickel(II)·perchlorate·methanol (6) and square planar (μ-hydroxo-μ-[2,6-bis[N-((S)-1-benzyl-2-yl-pyrrolidine)formimidoyl]p henolato]bisnickel(II)·bisperchlorate (7), are described. For the preparation of 7 a new 5-step route for homochiral bisamine (S)-benzyl-2-aminomethyl-pyrrolidine (19) was developed starting from (S)-proline. Epoxidation of unfunctionalized alkenes with sodium hypochlorite and tert-butyl hydroperoxide as terminal oxidants was effectively catalyzed with bisnickel(II)-complexes 6 and 7, and a turnover of 165 was reached using trans-β-methylstyrene (34). The epoxidations probably proceed via a radical intermediate (such as OCl·) and no enantioselectivity is obtained under phase transfer conditions. In epoxidation reactions employing tert-butyl hydroperoxide as terminal oxidant a turnover of 43 was obtained with trans-stilbene (30) as substrate. Unexpectedly in the case of styrene (29) 1,2-bis-(tert-butylperoxy)ethylbenzene (59) was isolated as the major product.
Lewis Acids as Activators in CBS-Catalysed Diels–Alder Reactions: Distortion Induced Lewis Acidity Enhancement of SnCl4
N?dling, Alexander R.,M?ckel, Robert,Tonner, Ralf,Hilt, Gerhard
, p. 13171 - 13180 (2016)
The effect of several Lewis acids on the CBS catalyst (named after Corey, Bakshi and Shibata) was investigated in this study. While2H NMR spectroscopic measurements served as gauge for the activation capability of the Lewis acids, in situ FT-IR spectroscopy was employed to assess the catalytic activity of the Lewis acid oxazaborolidine complexes. A correlation was found between the Δδ(2H) values and rate constants kDA, which indicates a direct translation of Lewis acidity into reactivity of the Lewis acid–CBS complexes. Unexpectedly, a significant deviation was found for SnCl4as Lewis acid. The SnCl4–CBS adduct was much more reactive than the Δδ(2H) values predicted and gave similar reaction rates to those observed for the prominent AlBr3–CBS adduct. To rationalize these results, quantum mechanical calculations were performed. The frontier molecular orbital approach was applied and a good correlation between the LUMO energies of the Lewis acid–CBS–naphthoquinone adducts and kDAcould be found. For the SnCl4–CBS–naphthoquinone adduct an unusual distortion was observed leading to an enhanced Lewis acidity. Energy decomposition analysis with natural orbitals for chemical valence (EDA-NOCV) calculations revealed the relevant interactions and activation mode of SnCl4as Lewis acid in Diels–Alder reactions.
Azetidine based ligands in boron catalyzed asymmetric
Starmans, Wim A. J.,Walgers, Richard W.A.,Thijs, Lambertus,De Gelder, Rene,Smits, Jan M.M.,Zwanenburg, Binne
, p. 4991 - 5004 (1998)
The preparation of a new class of azetidine-based auxiliaries and their selectivity in the BBr3 catalyzed Diels-Alder reaction is described. The results are compared with a similar proline-derived ligand and a known prolinol auxiliary. Results show that selectivities are highly dependent on the dienophile and the substituent of the chiral auxiliary.
Enantioselective Intermolecular [2+2] Photocycloaddition Reaction of Cyclic Enones and Its Application in a Synthesis of (-)-Grandisol
Poplata, Saner,Bach, Thorsten
, p. 3228 - 3231 (2018)
The intermolecular [2+2] photocycloaddition of typical cyclic α,β-unsaturated enones, such as 2-cyclohexenone, with olefins was performed in moderate to good yields (42-82%) and with high enantioselectivity (82%-96% ee). An unusual substitution pattern at the chiral oxazaborolidine-AlBr3 Lewis acid complex that promotes the reaction was found to be crucial for the success of the reaction. The method was applied to the enantioselective synthesis of the monoterpene (-)-grandisol, which could be accomplished in six steps and with an overall yield of 13% starting from 3-methyl-2-cyclohexenone.
Synthesis of W-propionylated (S)-(-)-2-(pyrrolidin-2-yl)propan2-ol and its use as a chiral auxiliary and selectivity marker in asymmetric aldol reactions
Hedenstroem, Erik,Andersson, Fredrik,Hjalmarsson, Mats
, p. 1513 - 1518 (2000)
The N-propionylated pyrrolidine derivative and chiral auxiliary, (S)-(-)-2-(pyrrolidin-2-yl)propan-2-ol, was synthesised and used in stereoselective aldol reactions with benzaldehyde. Differences in stereoselectivity were investigated as a function of temperature, solvent, chelating agent and the amount of the chelating agent used by monitoring the 1H NMR spectra of the aldol adducts that were obtained. Among the additives that were investigated, Cp2ZrCl2 induced higher syn-selectivity, while SnCl2 induced higher syn-selectivity respectively. TMSCl was found to induce high selectivity for one syn- and one anti-diastereomer. Varying the ligand sets on titanium additives was found to induce differences in selectivity, with (i-PrO)3TiCl exhibiting syn-selectivity and Cp2TiCl2 exhibiting anti-selectivity. Differences in reactivity and stereoselectivity were also found to depend upon the amount of Lewis acid that was added. Methods for removal of the auxiliary were also investigated. Acidic hydrolysis was used successfully to obtain the desired 3-hydroxy-2-methyl-3-phenylpropionic acids, but was found to give low yields and resulted in a large amount of epimerisation. Furthermore, the ethyl esters of these hydroxy acids are easy to separate into pure syn- and anti-diastereomers by LC. The Royal Society of Chemistry 2000.
Towards the Development of Frustrated Lewis Pair (FLP) Catalyzed Hydrogenations of Tertiary and Secondary Carboxylic Amides
K?ring, Laura,Paradies, Jan,Sitte, Nikolai A.
supporting information, p. 1287 - 1300 (2022/01/20)
The development of the frustrated Lewis pair catalyzed hydrogenation of tertiary and secondary amides is reviewed. Detailed insight into our strategies in order to overcome challenges during the reaction development process is provided. Furthermore, the d
London Dispersion Interactions Rather than Steric Hindrance Determine the Enantioselectivity of the Corey–Bakshi–Shibata Reduction
Eschmann, Christian,Song, Lijuan,Schreiner, Peter R.
, p. 4823 - 4832 (2021/02/01)
The well-known Corey–Bakshi–Shibata (CBS) reduction is a powerful method for the asymmetric synthesis of alcohols from prochiral ketones, often featuring high yields and excellent selectivities. While steric repulsion has been regarded as the key director of the observed high enantioselectivity for many years, we show that London dispersion (LD) interactions are at least as important for enantiodiscrimination. We exemplify this through a combination of detailed computational and experimental studies for a series of modified CBS catalysts equipped with dispersion energy donors (DEDs) in the catalysts and the substrates. Our results demonstrate that attractive LD interactions between the catalyst and the substrate, rather than steric repulsion, determine the selectivity. As a key outcome of our study, we were able to improve the catalyst design for some challenging CBS reductions.
Continuous flow heterogeneous catalytic reductive aminations under aqueous micellar conditions enabled by an oscillatory plug flow reactor
?tv?s, Sándor B.,Buchholcz, Balázs,Darvas, Ferenc,Kappe, C. Oliver,Novák, Zoltán,Sipos, Gellért,Wernik, Michaela
, p. 5625 - 5632 (2021/08/16)
Despite the fact that continuous flow processing exhibits well-established technical advances, aqueous micellar chemistry, a field that has proven extremely useful in shifting organic synthesis to sustainable water-based media, has mostly been explored under conventional batch-based conditions. This is particularly because of the fact that the reliable handling of slurries and suspensions in flow has been considered as a significant technical challenge. Herein, we demonstrate that the strategic application of an oscillatory plug flow reactor enables heterogeneous catalytic reductive aminations in aqueous micellar media enhancing mass transport and facilitating process simplicity, stability and scalability. The micellar flow process enabled a broad range of substrates, including amino acid derivatives, to be successfully transformed under reasonably mild conditions utilizing only very low amounts of Pd/C as a readily available heterogeneous catalyst. The preparative capabilities of the process along with the recyclability of the heterogenous catalyst and the aqueous reaction media were also demonstrated. This journal is
Synthesis of Optically Active N -(4-Hydroxynon-2-enyl)pyrrolidines: Key Building Blocks in the Total Synthesis of Streptomyces coelicolor Butanolide 5 (SCB-5) and Virginiae Butanolide A (VB-A)
Donges, Jonas,Hofmann, Sandra,Walter, Johannes C.,Reichertz, Julia,Brüggemann, Moritz,Frank, Andrea,Nubbemeyer, Udo
supporting information, p. 2632 - 2642 (2021/04/27)
Starting from 5-methylhexanal and (S)-configured N -propargylprolinol ethers, coupling delivered N -(4-hydroxynon-2-ynyl)prolinol derivatives as mixtures of C4 diastereomers. Resolution of the epimers succeeded after introduction of an (R)-mandelic ester derivative and subsequent HPLC separation. Alternatively, suitable oxidation gave the corresponding alkynyl ketone. Midland reagent controlled diastereoselective reduction afforded a defined configured propargyl alcohol with high selectivity. LiAlH 4reduction and Mosher analyses of the allyl alcohols enabled structure elucidation. The suitably protected products are used as key intermediates in enantioselective Streptomyces γ-butyrolactone signaling molecule total syntheses.
