- Photo-induced radical borylation of hemiacetals via C–C bond cleavage
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In this study, we reported a photo-induced radical borylation of hemiacetal derivatives via C–C bond cleavage. This transformation can be realized under mild conditions with simple reaction settings and irradiation of visible light. A series of substrates, including both cyclic and linear hemiacetal derivatives, were effectively transformed to the borylation product in moderate to good yields. Finally, the mechanism was studied in detail by DFT calculations, suggesting insight of the radical borylation process.
- Liu, Qianyi,Zhang, Jianning,Zhang, Lei,Mo, Fanyang
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supporting information
(2021/01/05)
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- Ruthenium-Promoted Acceptorless and Oxidant-Free Lactone Synthesis in Aqueous Medium
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Ruthenium-catalyzed formation of lactones from diols in aqueous medium has been demonstrated. 1,3,5-Triazaphosphaadamantane (PTA) included water-soluble ruthenium complexes [RuCl 2 (PPh 3)(2,6-Py-(CH 2 -PTA) 2 ]·2Br and [RuCl 2 (PPh 3) 2 (2-PyCH 2 PTA)]·Br in the presence of KOH were found to be efficient for the synthesis of lactones from diols. The reported synthetic protocol is green as it uses water as solvent, avoids the use of any hydrogen acceptor/oxidant, and produces hydrogen as the only side product. Mechanistic studies revealed that lactone formation involved aldehyde intermediate and followed dehydrogenative pathway.
- Bhatia, Anita,Kannan, Muthukumar,Muthaiah, Senthilkumar
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supporting information
p. 721 - 725
(2019/03/26)
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- Two Types of Cross-Coupling Reactions between Electron-Rich and Electron-Deficient Alkenes Assisted by Nucleophilic Addition Using an Organic Photoredox Catalyst
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Two types of photoreactions between electronically differentiated donor and acceptor alkenes assisted by nucleophilic addition using an organic photoredox catalyst efficiently afforded 1:1 or 2:1 cross-coupling adducts. A variety of alkenes and alcohols were employed in the photoreaction. Control of the reaction pathway (i.e., the formation of the 1:1 or 2:1 adduct) was achieved by varying the concentration of the alcohol used. Detailed mechanistic studies suggested that the organic photoredox catalyst acts as an effective electron mediator to promote the formation of the cross-coupling adducts.
- Tanaka, Yosuke,Kubosaki, Suzuka,Osaka, Kazuyuki,Yamawaki, Mugen,Morita, Toshio,Yoshimi, Yasuharu
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p. 13625 - 13635
(2018/09/25)
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- Bent bonds (τ) and the antiperiplanar hypothesis, and the reactivity at the anomeric center in pyranosides
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The stereoselectivity of nucleophilic addition on oxocarbenium ions derived from the bicyclic pyranoside model with or without a C2-OR group can be understood through the use of the bent-bond and the antiperiplanar hypothesis in conjunction with the concept of hyperconjugation as an alternative interpretive model of structure and reactivity.
- Parent, Jean-Fran?ois,Deslongchamps, Pierre
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p. 11183 - 11198
(2016/12/09)
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- Hydrogenation of coumarin to octahydrocoumarin over a Ru/C catalyst
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The production of octahydrocoumarin, which can serve as a replacement for toxic coumarin, was investigated using 5% Ru on active carbon (Ru/C) as the catalyst for the hydrogenation of coumarin. The hydrogenation was studied by optimizing the reaction conditions (pressure, solvent and coumarin concentration). The activity and selectivity of the Ru/C catalyst were compared for different solvents. The mechanism of coumarin hydrogenation was deduced. The formation of side products was explained. The optimal hydrogenation reaction conditions were: 130 °C, 10 MPa, 60 wt% coumarin in methanol, and 0.5 wt% (based on coumarin) of Ru/C catalyst. At the complete conversion of coumarin, the selectivity to the desired product was 90%.
- Bílková, Dana,Jansa, Petr,Paterová, Iva,?erveny, Libor
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p. 957 - 960
(2015/07/01)
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- Stereocontrolled synthesis of substituted bicyclic ethers through oxy-Favorskii rearrangement: Total synthesis of (±)-communiol e
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The potential of the oxy-Favorskii rearrangement to form branched cis-fused bicyclic ethers was explored. Both tertiary and quaternary centers were constructed in highly stereospecific manners. Methanol and primary amines were effective nucleophiles for the rearrangement. The total synthesis of (±)-communiol E was achieved based on this method.
- Kobayashi, Shoji,Kinoshita, Tatsuhiro,Kawamoto, Takuji,Wada, Masato,Kuroda, Hiroyuki,Masuyama, Araki,Ryu, Ilhyong
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p. 7096 - 7103
(2011/10/31)
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- NHC-catalyzed ring expansion of oxacycloalkane-2-carboxaldehydes: A versatile synthesis of lactones
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Imidazolinium-derived carbenes catalyze the ring-expansion lactonization of oxacycloalkane-2-carboxaldehydes. A variety of functionalized five-, six-, and seven-membered lactones can be formed efficiently under mild reaction conditions. The success of this new method for the construction of lactones is highly influenced by the electronic nature of the carbene catalyst.
- Wang, Li,Thai, Karen,Gravel, Michel
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supporting information; experimental part
p. 891 - 893
(2009/08/15)
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- Synthesis of γ- and δ-lactones from alkynols
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The reaction of alkynyl phenyl selenides with p-toluene-sulfonic acid gives rise to a proton-induced ring-closure reaction affording γ- and δ-lactones. Georg Thieme Verlag Stuttgart.
- Tiecco, Marcello,Testaferri, Lorenzo,Temperini, Andrea,Terlizzi, Raffaella,Bagnoli, Luana,Marini, Francesca,Santi, Claudio
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p. 587 - 590
(2007/10/03)
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- Compounds having protected hydroxy groups
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The present invention relates to compounds with protected hydroxy groups of formula (I) These compounds are precursors for organoleptic agents, such as fragrances, and masking agents and for antimicrobial agents. When activated, the compounds of formula (I) are cleaved and form one or more organoleptic and/or antimicrobial compounds.
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- Compounds having protected hydroxy groups
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The present invention relates to compounds with protected hydroxy groups of formula (I) These compounds are precursors for organoleptic agents, such as fragrances, and masking agents and for antimicrobial agents. When activated, the compounds of formula (I) are cleaved and form one or more organoleptic and/or antimicrobial compounds.
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- Stereoselective synthesis of δ-lactones from 5-oxoalkanals via one-pot sequential acetalization, tishchenko reaction, and lactonization by cooperative catalysis of samarium ion and mercaptan
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By the synergistic catalysis of samarium ion and mercaptan, a series of 5-oxoalkanals was converted to (substituted) δ-lactones in efficient and stereoselective manners. This one-pot procedure comprises a sequence of acetalization, Tishchenko reaction and lactonization. The deliberative use of mercaptan, by comparison with alcohol, is advantageous to facilitate the catalytic cycle. The reaction mechanism and stereochemistry are proposed and supported by some experimental evidence. Such samarium ion/mercaptan cocatalyzed reactions show the feature of remote control, which is applicable to the asymmetric synthesis of optically active δ-lactones. This study also demonstrates the synthesis of two insect pheromones, (2S,5R)-2-methylhexanolide and (R)-hexadecanolide, as examples of a new protocol for asymmetric reduction of long-chain aliphatic ketones.
- Hsu,Fang
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p. 8573 - 8584
(2007/10/03)
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- Microbial bioreductions of γ- and δ-ketoacids and their esters
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A series of yeasts were used in the bioreductions of aliphatic and aromatic γ- and δ-ketoacids and esters to investigate the preparation of enantiomerically pure γ- and δ-lactones through the intermediacy of their corresponding γ- and δ-hydroxyacids and esters. Bioreduction of ethyl 4-oxononanoate 2a with Pichia etchellsii afforded the γ-nonanolide (+)-5a with 99% e.e., while Pichia minuta proved to be the best choice for the bioreduction of ethyl 2-oxocyclohexylacetate 2e, which afforded cis-(-)-5e and trans-(-)-5e with 98 and 99% e.e., respectively. Reduction of 3-(2-oxocyclohexyl)propionic acid 3e with Pichia glucozyma gave predominantly the corresponding δ-lactone trans-(-)-6e with 94% e.e., whose absolute configuration was determined by means of CD spectroscopy.
- Forzato, Cristina,Gandolfi, Raffaella,Molinari, Francesco,Nitti, Patrizia,Pitacco, Giuliana,Valentin, Ennio
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p. 1039 - 1046
(2007/10/03)
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- Precursor compounds
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The compounds of the formula I are precursors for organoleptic and antimicrobial compounds. The latter are generated in the presence of skin bacteria, enzymes or acidic or alkaline conditions. One precursor molecule can provide one or more different compounds.
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- Beta-ketoester compounds
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The beta-ketoesters of formula I are useful as precursors for organoleptic compounds, especially for flavors, fragrances and masking agents and antimicrobial compounds.
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- Selective generation of free radicals from epoxides using a transition-metal radical. A powerful new tool for organic synthesis
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Bis(cyclopentadienyl)titanium(III) chloride reacts with epoxides by initial C-O homolysis. The regiochemistry of the opening is determined by the relative stabilities of the radicals. Depending on the reaction partners, these radicals undergo intramolecular (hex-5-enyl cyclization) or intermolecular additions to olefins. The resultant radicals are efficiently scavenged by a second equivalent of Ti(III) to afford the corresponding Ti(IV) derivative. Treatment of this intermediate with electrophiles such as H+ or halogens provides a route to functionalized cyclopentanes and other useful products. The radical initially formed from an epoxide can also be trapped by H-atom donors such as 1,4-cyclohexadiene or tert-butyl thiol, resulting in an overall reduction of the epoxide. In the absence of a H-atom donor or an olefin, this radical is trapped by Ti(III), resulting in a β-oxido-Ti organometallic species which undergoes facile elimination to give an olefin. The reaction conditions are remarkably mild and are applicable to very sensitive substrates.
- RajanBabu,Nugent, William A.
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p. 986 - 997
(2007/10/02)
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- Conversion of 5-oxoalkanals to δ-lactones by an intramolecular Tishchenko reaction
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Diisobutylaluminum hydride reduction of photoadducts 3 (7,8-tri- and tetrasubstituted l,3,3-trimethyl-2,4-dioxabicyclo-[4.2.0]octan-5-ones), derived from 2,2,6-trimethyl-4/f-l,3-dioxin-4-one (1), gave 6-lactones 7 in good to excellent yields if the workup involved a methanol quench followed by removal of the solvent. We propose that the reaction proceeds by an intramolecular Tishchenko reaction of the intermediate 5-oxoalkanal 5 and is catalyzed by the Lewis acid diisobutylaluminum methoxide, 8. A deuterium labelling experiment supports the mechanistic proposal and the conversion of 5-oxoalkanals other than S illustrates the scope of the procedure. To our knowledge, this is the first report of a true intramolecular Tishchenko reaction.
- Lange, Gordon L.,Organ, Michael G.
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p. 665 - 667
(2018/06/18)
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- ENZYMATIC RESOLUTION OF RACEMIC BICYCLIC LACTONES BY HORSE LIVER ESTREASE
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Optically active lactones were prepared by Horse Liver esterase catalyzed hydrolysis of bicyclic γ-butyrolactones.
- Guibe-Jampel, E.,Rousseau, G.,Blanco, L.
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- OXIDATIVE BISDECARBOXYLATION OF α-ALKOXYMALONIC ACIDS WITH CERIUM(IV)
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Ceric ammonium nitrate is an excellent reagent for preparing carboxylic esters from α-alkoxymalonic acids by oxidative bisdecarboxylation.
- Salomon, Robert G.,Roy, Subhas,Salomon, Mary F.
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p. 769 - 772
(2007/10/02)
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- Synthetic and Stereochemical Studies of the Octahydro-1-benzopyran System
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The cis and trans isomers of the octahydro-1-benzopyran system have been synthesised and their conformations studied by low-temperature (13)C and highfield (1)H n.m.r. spectroscopy.The position of the conformational equilibrium in the cis isomer at -70 deg C in CDCl3-CFCl3 (50:50) has been determined as approximately 99.5:0.5 (ΔG0 -8.9 kJ mol-1) in favour of the conformation having the oxygen axially disposed towards the cyclohexane ring.
- Griffiths, D. Vaughan,Wilcox, Geoffrey
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p. 431 - 436
(2007/10/02)
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- Stereochemical studies. X. Synthesis of some epimeric δ-lactones
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Stereospecific synthesis are reported for the δ-lactones 3, 5, 8, 17, and 26.
- Cooke, Ellen,Paradellis, Themistocles C.,Edward John T.
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- Stereochemical studies. XI. Equilibria between δ-hydroxy-acids and δ-lactones in aqueous tetrahydrofuran. Relative stabilities of isomeric δ-lactones
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The equilibrium constants K' for the hydrolysis of 13 δ-lactones to hydroxy-acids in 54percent (mol/mol) aqueous tetrahydrofuran at 25 deg C have been determined.The equilibrium constants for the isomerization of the five δ-lactones into their epimers, and for the isomerization of their hydroxy-acids into their epimers, have been calculated by the methods of conformational analysis.These calculated values are consistent with the experimental values of K'.Addition of methyl groups to a hydroxy-acid decreases K' (the Thorpe-Ingold effect).
- Edward, John T.,Cooke, Ellen,Paradellis, Themistocles C.
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p. 2546 - 2553
(2007/10/02)
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