- A Catalytic Asymmetric Ene Reaction for Direct Preparation of α-Hydroxy 1,4-Diketones as Intermediates in Natural Product Synthesis
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Asymmetric access to α-hydroxy-1,4-diketones has been achieved by direct ene coupling of silyl enol ethers with glyoxal electrophiles, mediated by a chiral N, N ′-dioxide-nickel(II) complex catalyst. Successful union of a polyketide silyl enol ether with an α-quaternary glyoxal, generated by dioxirane oxidation of an α-diazo ketone, models a proposed C 5 -C 6 disconnection of the polyketide and spirocyclic imine domains of the marine natural product, portimine.
- Aitken, Harry R. M.,Brimble, Margaret A.,Furkert, Daniel P.
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- Organocatalytic enantioselective total synthesis of (-)-arboricine
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The tetracyclic indole alkaloid (-)-arboricine has been prepared using an asymmetric organocatalytic Pictet - Spengler reaction as the key step followed by a diastereoselective Pd-catalyzed iodoalkene/enolate cyclization. The absolute stereochemistry was unequivocally proven by X-ray crystallographic analysis and appeared to be opposite to the published structure in the original paper.
- Wanner, Martin J.,Boots, Rowan N.A.,Eradus, Bram,De Gelder, Rene,Van Maarseveen, Jan H.,Hiemstra, Henk
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- (5 E/ Z,7 E,9)-Decatrien-2-ones, Pineapple-like Flavors from Fomitopsis betulina - Structure Elucidation and Sensorial Properties
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During the cultivation of the edible mushroom Fomitopsis betulina on agro-industrial side streams, a pleasant flavor strongly reminiscent of pineapple was perceived. Aroma extract dilution analyses identified two flavor components with a distinct pineapple odor. On the basis of mass spectrometric data, a Wittig reaction of (E)-penta-2,4-dien-1-yltriphosphonium bromide with ethyl levulinate was conducted. The resulting (5E/Z,7E,9)-decatrien-2-ones were identical to the compounds isolated from the fungal culture. Some structurally related methyl ketones were synthesized, confirmed by nuclear magnetic resonance and mass spectrometry, and their odor was characterized. The lowest odor threshold and most characteristic pineapple-like odor was found for (5Z,7E,9)-decatrien-2-one. Global minimum energy calculation of the methyl ketones and the comparison to (1,3E,5Z)-undecatriene, a character impact compound of fresh pineapple, showed that a chain length of at least 10 carbon atoms and a terminal double bond embedded in a "L"-shaped conformation were common to compounds imparting an intense pineapple-like odor. Both (5E/Z,7E,9)-decatrien-2-ones have not been described as natural flavor compounds.
- Grosse, Miriam,Pendzialeck, Tim,Fohrer, Jorg,Berger, Ralf G.,Krings, Ulrich
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p. 10329 - 10335
(2019/12/30)
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- Concise catalytic asymmetric total synthesis of biologically active tropane alkaloids
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A general strategy for the total asymmetric synthesis of valuable tropane alkaloids by catalytic stereoselective transformations is disclosed. The power of this approach is exemplified by the concise catalytic enantioselective total syntheses of (+)-methylecgonine, (-)-cocaine and (+)-cocaine as well as the first catalytic asymmetric total syntheses of a cocaine C-1 derivative and (+)-ferruginine starting from 5-oxo-protected-α,β-unsaturated enals using only two and three column chromatographic purification steps, respectively. Copyright
- Cordova, Armando,Lin, Shuangzheng,Tseggai, Abrehet
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supporting information; experimental part
p. 1363 - 1372
(2012/06/18)
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- Enantioselective hydroformylation of N-vinyl carboxamides, allyl carbamates, and allyl ethers using chiral diazaphospholane ligands
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Rhodium complexes of diazaphospholane ligands catalyze the asymmetric hydroformylation of N-vinyl carboxamides, allyl ethers, and allyl carbamates; products include 1,2- and 1,3-aminoaldehydes and 1,3-alkoxyaldehydes. Using glass pressure bottles, short reaction times (generally less than 6 h), and low catalyst loading (commonly 0.5 mol %), 20 substrates are successfully converted to chiral aldehydes with useful regioselectivity and high enantioselectivity (up to 99% ee). Chiral Roche aldehyde is obtained with 97% ee from the hydroformylation of allyl silyl ethers. Commonly difficult substrates such as 1,1- and 1,2-disubstituted alkenes undergo effective hydroformylation with 89-97% ee and complete conversion for six examples. Palladium-catalyzed aerobic oxidative amination of allyl benzyl ether followed by enantioselective hydroformylation yields the β3-aminoaldehyde with 74% ee.
- McDonald, Richard I.,Wong, Gene W.,Neupane, Ram P.,Stahl, Shannon S.,Landis, Clark R.
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supporting information; experimental part
p. 14027 - 14029
(2011/01/04)
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- Preparation of bicyclic 1,2,4-trioxanes from γ,δ-unsaturated ketones
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(Chemical Equation Presented) Treatment of γ,δ-unsaturated ketones with hydrogen peroxide and acid provides a rapid entry into the medicinally important 1,2,4-trioxane structure. Alkene substitution that stabilizes carbocationic intermediates proved to be important for the success of this transformation.
- Ramirez, Armando P.,Thomas, Andrew M.,Woerpel
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supporting information; experimental part
p. 507 - 510
(2009/08/07)
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- Triquinanes from linear ketones via trimethylenemethane diyls
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Linear compounds containing a ketone and diene functional groups reacted with the anion of TMS-diazomethane to produce alkylidene carbenes that underwent intramolecular cyclopropanation followed by the formation of trimethylenemethane diyls which underwent [2+3] cycloaddition reaction to produce linearly fused triquinanes.
- Lee, Hee-Yoon,Kim, Won-Yeob,Lee, Sejin
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p. 1407 - 1410
(2007/10/03)
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- Facile entry to substituted decahydroquinoline alkaloids. Total synthesis of lepadins A-E and H
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Condensation of a L-alanine derived δ-bromo-β-silyloxy- propylamine with 1,3-cyclohexadione followed by alkylative cyclization produces a bicyclic enone. Diastereoselective Pt/C-catalyzed hydrogenation of this enone in HOAc provides a 5-oxo-cis-fused decahydroquinoline. Wittig olefination of this decahydroquinoline and subsequent epimerization of the resulting 5-formyl intermediate gives rise to a 5-β-formyl decahydroquinoline exclusively. In a parallel procedure, Peterson reaction of this decahydroquinoline and subsequent hydrogenation of the generated 5-exo-olefin provides a decahydroquinoline with a 5-α-substituent predominantly. For these two diastereoselective processes, using the intermediates without N-protection as the substrates is essential because the corresponding N-Boc intermediates give poor diastereoselectivity. The intermediate with β-form side chain is further converted into lepadins A-C via carbon chain elongation, while the intermediate with α-form side chain is transformed into lepadins D, E, and H and corresponding 5′-epimers via connection with two sulfones generated from two Sharpless epoxidation products. By comparison of the rotations and NMR data, the stereochemistry of lepadins D, E, and H is assigned as 2S,3R,4aS,5S,8aR,5′R.
- Pu, Xiaotao,Ma, Dawei
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p. 6562 - 6572
(2007/10/03)
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- The DDQ mediated cyclization products of some 2-hydroxy-3(1′-alkenyl)-1,4-naphthoquinones
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The DDQ mediated cyclisation products derived from 2-hydroxy-3-(1′-alkenyl)-1,4-napthoquinones viz. 17 were found to be temperature dependent. At 60°C the naphthofuranquinone 19 was the predominant isomer whereas at 8°C the naphthopyranquinone 18 was exclusively formed.
- Ameer, Farouk,Giles, Robin G.F.,Green, Ivan R.,Nagabhushana, Kyatanahalli S.
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p. 369 - 380
(2007/10/03)
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- Tandem hemiketal formation-intramolecular Friedel-Crafts alkylation: A facile route to hetero-atom-substituted benzo-fused bicyclo[3.3.1]nonanes
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A previously unknown intramolecular Friedel-Crafts alkylation with in situ formed hemiketals as the electrophile is reported.
- Wu, Yikang,Li, Yan,Wu, Yu-Lin
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p. 163 - 171
(2007/10/03)
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- The First Tandem [2 + 2] Cycloaddition-Michael Reaction Using Ynolates: Facile Construction of Substituted Carbocycles
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(matrix presented) A tandem [2 + 2] cycloaddition-Michael reaction using ynolate anions followed by decarboxylation produced polysubstituted five-, six-, and seven-membered cycloalkenes.
- Shindo, Mitsuru,Matsumoto, Kenji,Sato, Yusuke,Shishido, Kozo
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p. 2029 - 2030
(2007/10/03)
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- Masked oxo sulfinimines (N-sulfinyl imines) in the asymmetric synthesis of proline and pipecolic acid derivatives.
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[structure: see text]. On addition of Et2AlCN/i-PrOH, masked oxo sulfinimines give alpha-amino nitriles that afford oxo alpha-amino acids on hydrolysis. These amino acids cyclize and are reduced to cis proline and cis pipecolic acids derivatives in high ee and good yield. This new procedure avoids many of the limitations related to the preparation of oxo amino acids from proteinogenic amino acids.
- Davis,Zhang,Lee
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p. 759 - 762
(2007/10/03)
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- Reductive Cyclization of Ketones Tethered to Activated Olefins Mediated by Magnesium in Methanol
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The reductive cyclization of various ketones tethered to activated olefins such as α,β-unsaturated esters, nitriles, sulfoxides, and sulfides mediated by magnesium in dry methanol in the presence of mercuric chloride.When traeted with magnesium in dry methanol at -23 deg C all of the ketones except nitrile 9 (42percent) and 5-oxa-8-keto-2-enoate 5 (13percent) gave excellent yields (79-98percent) of mono- and bicyclic alcohol products resulting from carbon-carbon bond formation between the β-carbon of the activated olefin and the carbonyl carbon.The reaction was accelerated by the catalytic amount of mercuric chloride, although the stereoselectivity was not affected by the catalyst.For all the substrates except 8-keto-2-enoate 3 and 5-aza-8-keto-2-enoate 6, the configuration of the major product was trans between the hydroxy and (methoxycarbonyl)methyl groups.The product isomer ratios were independent of the substrate geometry (E or Z).In contrast to the ketones, aldehydes tethered to α,β-unsaturated esters gave products of simple reduction of the double bond and/or saturated alcohols instead of the cyclized products.When the reaction temperature was lowered, the yields of cyclized product were significantly affected by the production of appreciable amounts of saturated product, but the stereoselectivity was not improved.Under the same reaction conditions α,β-unsaturated sulfoxide 16 gave deoxygenated sulfide 18 (85percent) as the major product along with a small amount (9percent) of cyclized product 19t.In contrast, sulfone 17 underwent desulfonylation instead of cyclization to give olefin 20 (54percent).With excess magnesium (15 equiv), however, α,β-unsaturated sulfoxide 16 gave cyclized sulfide 19t (95percent) via deoxygenated sulfide 18.Both 16Z and 16E afforded product 19t as a single isomer.It is suggested that the reductive cyclization of the α,β-unsaturated esters and nitriles proceed by means of nucleophilic attack of a β-carbon radical anion, formed by initial electron transfer from magnesium metal to the activated olefin, on the carbonyl group.The cyclization of the α,β-unsaturated sulfide proceeds by nucleophilic attack of the ketyl on the olefinic double bond.
- Lee, Ge Hyeong,Choi, Eun Bok,Lee, Eun,Pak, Chwang Siek
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p. 1428 - 1443
(2007/10/02)
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- Marschalk reaction approaches for the synthesis of (+/-)-4-demethoxydaunomycinone
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Marschalk reaction on leucoquinizarin (10) with the appropiate aldehydes 6 or 8 affords the alkylated quinizarin derivatives 11b and 13b respectively which are succesfully elaborated to 4-demethoxy-7,9-dideoxydaunomycinone (4) Marschalk reaction of 10 with bromoaldehyde 9, directly gives 4. 2-Formylquinizarin (21) and levulinic aldehyde 7 under the Marschalk reaction gives 8-acetyl-6,11-dihydroxy-9,10-dihydro-5,12-naphthacenedione (22), a useful intermediate for the asymmetric synthesis of (-)-4-demethoxy-7-deoxydaunomycinone.
- Ayyangar, N R,Argade, A B,Mehendale, A R,Deshpande, V H
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- SYNTHESIS OF THE PHEROMONES, (E)-3,7-DIMETHYL-2,7-OCTADIENYL PROPIONATE, (E)-3,7-DIMETHYL-2-OCTENE-1,8-DIOL AND FRONTALIN FROM A COMMON INTERMEDIATE
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Ketal ester 9 has been prepared in five steps from methyl levulinate 4 (scheme 1).The propionate 1, diol 2 and (+/-) frontalin 3 were prepared from ester 9 employing the routes shown in scheme 2,3 and 4 respectively.The branched chain alkenes 13 and 20 were prepared conveniently from the primary alcohols 11 and 10 following the procedure of S.Wolff.Triethyl phosphonopropionate 7 has been prepared by methylating triethylphosphonoacetate with methyl iodide in the presence of sodium hydride.
- Dhokte, U. P.,Rao, A. S.
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p. 811 - 822
(2007/10/02)
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- Thromboxane A2 Analogues from 8-Oxabicyclooct-6-en-3-ones
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We describe approaches to thromboxane A2 analogues (3), (4), and (32) which contain 2,6-dioxabicyclooctane and 2,6-dioxatricyclo3,7>nonane ring system.Both were derived from 2-substituted 8-oxabicyclooct-6-en-3-
- Bowers, Kevin G.,Mann, John,Walsh, E. Brian,Howarth, Oliver W.
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p. 1657 - 1666
(2007/10/02)
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- DABCO-Catalyzed Coupling of Aldehydes with Activated Double Bonds. 4. Stereoselective Synthesis of Trisubstituted Olefins and Terpenoid Building Blocks via 2-(Hydroksyalkyl)-2-propenoic Esters.
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A variety of 2-(hydroksyalkyl)-2-propenoic esters 16a-g has been prepared in high yield by DABCO-catalyzed coupling of aldehydes 14a-g with methyl acrylate.The product esters 16a-g are useful building blocks in syntheses which undergo regioselective and Z-selective SN2 reactions with N-bromosuccinimide/dimethyl sulfide and N-chlorosuccinimide/dimethyl sulfide to furnish (Z)-2-(bromomethyl)-2-alkenoic esters 17a-g and (Z)-2-(chloromethyl)-2-alkenoic esters 18b,c,d, respectively.Similarly, the derived allylic acetates 21g,h, and also allylic bromide 17g react with lithium triethylhydridoborate via mechanism SN2' to give (E)-2-methyl-2-alkenoic esters 22g,h and respectively, 2-methylenealkanoic esters 20g.Methyl (Z)-6,6-(ethylenedioxy)-2-methyl-2-heptenoate (22h) has been prepared as an intermediate en route to the norsesquiterpenoid ketone 23.The allylic bromides 17d,e,f also furnish (Z)-6-methyl-5--4-heptene-1,6-diol (19a), (Z)-2-methyl-3--3-octene-2,7-diol (19e), and (Z)-7-methyl-6--5-octene-1,2,7-triol (19f), which are terpenoid building blocks.
- Hoffmann, H. Martin R.,Rabe, Juergen
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p. 3849 - 3859
(2007/10/02)
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- Stereoselective syntheses of Sex Pheromone of Mediterranean Fruitfly and Alarm Pheromone of Ants
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Facile synthetic routes to the sex pheromone components (Ia and Ib) of Mediterranean fruitfly, and te alarm pheromone (II) of ants in various species, are described.The key intermediates (1 and 2) for these syntheses, are derived from tetrahydrofurfuryl alcohol.Bromination of 1, and alkylation of dimethyl malonate with the resulting bromide (3), lead to Ia which on LAH reduction affords Ib.Whereas, oxidation of 2 followed by olefination with (i-propylidene)triphenylphosphorane, and subsequent deketalisation completes the synthesis of II.
- Joshi, N. N.,Mamdapur, V. R.,Chadha, M. S.
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p. 577 - 579
(2007/10/02)
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