- Total synthesis and stereochemical revision of the chlorinated sesquiterpene (±)-gomerone C
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Red algae from the genus Laurencia (Ceramiales) are the source of over 500 halogenated terpenes, cyclic ethers, and acetogenides, which in some cases have been suggested to serve as chemical defence agents because of their activity against pathogenic marine bacteria and herbivores. In 2008 a Spanish research group reported the isolation and structural elucidation of three novel chlorinated sesquiterpenes, gomerones A-C, from samples of Laurencia majuscula collected at the southern coast of La Gomera, Canary Islands (Scheme 1). The structurally interesting and unprecedented gomerane skeleton in combination with their unexplored biological activity as well as the halogenated nature of these natural products rendered them noteworthy targets for synthesis. Herein, we report a total synthesis of gomerone C (1), which not only represents the first synthesis of a member of this novel class of chlorinated sesquiterpenes, but also resulted in the revision of the relative stereochemistry of gomerone C (1) and hence to a stereochemical reassignment of gomerone B (2).
- Huwyler, Nikolas,Carreira, Erick M.
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- Substituted cis-hydrindan-4-ones by sequential cycloadditions
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The synthesis of substituted cis-hydrindan-4-ones is reported. Particular emphasis was placed on the diastereoselective construction of quaternary stereogenic ring carbon atoms. An intermolecular asymmetric Al(III)-promoted (4+2)-cycloaddition served as the principal C/C-connecting tool. Opportunities for the further structural elaboration of the (4+2)-cycloadducts were explored.
- Steffen, Sara,Sch?fer, Andreas,Hiersemann, Martin
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p. 3489 - 3504
(2015/11/17)
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- The intramolecular Morita-Baylis-Hillman-type alkylation reaction
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From the initial development of a homologous Morita-Baylis-Hillman reaction utilizing epoxides as electrophiles, the method was expanded to enable the exclusively organocatalyzed intramolecular allylation of enones and to develop the intramolecular MBH-type alkylation of activated alkenes. We successfully utilized both enones and unsaturated thioesters as the activated alkene component. This work, carried out using stoichiometric amounts of the trialkylphosphine, gave an array of functionalized five- and six-membered carbocycles in high yields. With the cycloalkylation of enones and thioesters, conditions that allowed the use of substoichometric amounts of the phosphine catalyst were developed. As a result both five- and six-membered rings can be formed efficiently with little to no loss in yield upon comparison to yields obtained when stoichiometric amounts of trialkylphosphines were employed. We isolated, for the first time, an MBH-type intermediate exhibiting unprecedented trans geometry of the phosphonium salt and acyl group.
- Cran, John W.,Krafft, Marie E.,Seibert, Kimberly A.,Haxell, Thomas F.N.,Wright, James A.,Hirosawa, Chitaru,Abboud, Khalil A.
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experimental part
p. 9922 - 9943
(2012/02/05)
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- Palladium-catalyzed asymmetric alkylation in the synthesis of cyclopentanoid and cycloheptanoid core structures bearing all-carbon quaternary stereocenters
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General catalytic asymmetric routes toward cyclopentanoid and cycloheptanoid core structures embedded in numerous natural products have been developed. The central stereoselective transformation in our divergent strategies is the enantioselective decarboxylative alkylation of seven-membered β-ketoesters to form α-quaternary vinylogous esters. Recognition of the unusual reactivity of β-hydroxyketones resulting from the addition of hydride or organometallic reagents enabled divergent access to γ-quaternary acylcyclopentenes through a ring contraction pathway or γ-quaternary cycloheptenones through a carbonyl transposition pathway. Synthetic applications of these compounds were explored through the preparation of mono-, bi-, and tricyclic derivatives that can serve as valuable intermediates for the total synthesis of complex natural products. This work complements our previous work with cyclohexanoid systems.
- Hong, Allen Y.,Bennett, Nathan B.,Krout, Michael R.,Jensen, Thomas,Harned, Andrew M.,Stoltz, Brian M.
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p. 10234 - 10248
(2012/01/03)
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- Organocatalysis of the Morita-Baylis-Hillman alkylation using trialkylphosphines
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Using a catalytic amount of trialkylphosphines, alkyl halides undergo efficient intramolecular Morita-Baylis-Hillman cyclization. Georg Thieme Verlag Stuttgart.
- Krafft, Marie E.,Seibert, Kimberly A.
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p. 3334 - 3336
(2008/09/17)
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- Isomerization of propargylic alcohols into α,β-unsaturated carbonyl compounds catalyzed by the sixteen-electron allyl-ruthenium(II) complex [Ru(η3-2-C3H4Me)(CO)(dppf)] [SbF 6]
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The 16-e- (η3-allyl)-ruthenium(II) complex [Ru(η3-2-C3H4Me)(CO)(dppf)][SbF 6] is an efficient catalyst for the regioselective isomerization of terminal propargylic alcohols HC≡CCR1R2(OH) into α,β-unsaturated aldehydes R1R2C=CHCHO or ketones R3R4C=C(R1)COMe (if R2 = CHR3R4) under mild conditions. This complex has been also used as catalyst for the preparation of conjugated 1,3-enynes via dehydration of propargylic alcohols.
- Cadierno, Victorio,Garcia-Garrido, Sergio E.,Gimeno, Jose
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p. 101 - 110
(2007/10/03)
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- Unprecedented reactivity in the Morita-Baylis-Hillman reaction; intramolecular α-alkylation of enones using saturated alkyl halides
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sp3 Hybridized electrophiles, never before used in the organo-mediated Morita-Baylis-Hillman reaction, now facilitate the formation of five- and six-membered enone cycloalkylation products. The Royal Society of Chemistry 2005.
- Krafft, Marie E.,Seibert, Kimberly A.,Haxell, Thomas F. N.,Hirosawa, Chitaru
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p. 5772 - 5774
(2007/10/03)
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- Application of Rh(l)-Catalyzed C - H Bond Activation to the Ring Opening of 2-Cycloalkenones in the Presence of Amines
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(matrix presented) Herein described is the application of the Rh(l)-catalyzed C-H bond activation to the ring-opening of 2-cycloalkenones in the presence of cyclohexylamine. This reaction includes the C-C double bond cleavage of 2-cycloalkenones through the conjugate addition of cyclohexylamine followed by the retro-Mannich-type fragmentation. The resulting ring-opened intermediates subsequently underwent either chelation-assisted hydroacylation to afford a ring-opened dicarbonyl compound or β-alkylation via a ring contraction.
- Jun, Chul-Ho,Moon, Choong Woon,Lim, Sung-Gon,Lee, Hyuk
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p. 1595 - 1597
(2007/10/03)
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- Facile approach to versatile chiral intermediates for fused cyclopentanoid natural products
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A facile approach to cis- and trans-2-(1-hydroxymethyl)vinyl-1-vinylcyclohexan-1-ols and to the corresponding cyclopentane, cycloheptane, and cyclooctane derivatives has been developed, starting from cycloalkanones involving the key steps of Rupe and Claisen orthoester rearrangements. The formation of intervening products could be explained by allylic strain and π-stacking, respectively.
- Zulfiqar, Fazila,Malik, Abdul
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p. 1227 - 1234
(2007/10/03)
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- Siloxyalkyne - Alkene metathesis: Rapid access to highly functionalized enones
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Mechanistically intriguing participation of siloxyalkynes occurs in the intramolecular Ru-catalyzed metathesis with terminal alkenes (see scheme; Ms = methanesulfonyl). Combined with efficient protodesilylation, this process resulted in the development of a new method for the synthesis of highly functionalized enones starting from readily accessible acyclic precursors. Heterocyclic and polycyclic compounds were prepared efficiently, which illustrates the generality of this novel method.
- Schramm, Michael P.,Srinivasa Reddy,Kozmin, Sergey A.
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p. 4274 - 4277
(2007/10/03)
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- Phenol catalyzed Claisen ortho ester rearrangment of allylic alcohols with trimethyl-β-(methoxy) ortho propionate
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Phenol catalyzed Claisen ortho ester rearrangment of allylic alcohols with trimethyl-β-(methoxy) ortho propionate can be affected in relatively quick time and lower temperature with only 1.5 equivalents of ortho ester. The rearrangement does not experience undesirable side reactions reported earlier in literature [3].
- Iqbal, Fazila,Ateeq, Humayun S.,Malik, Abdul,Zeeshan,Ali, Zulfiqar
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p. 1244 - 1245
(2007/10/03)
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- Highly stereoselective synthesis of bicyclo[n.3.0]alkanes by titanium tetrachloride promoted [3 + 2] cycloaddition of allylsilanes and 1-acetylcycloalkenes
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The titanium tetrachloride promoted reaction of allylsilanes 1 with 1-acetylcyclohexene is shown to afford the silylbicyclo[4.3.0]nonanes 9 ([3 + 2] cycloaddition products) along with the 1-acetyl-2-allylcyclohexane 4 (Hosomi-Sakurai product). Here we report that systematic variation of the substituents at the silicon atom of 1 allows suppression of the classical Hosomi Sakurai reaction in favor of the [3+2] cycloaddition. Cycloaddition of the allylsilanes 1d, 1i, and 1k with 1-acetylcycloalkenes 10, containing a 5-, 6-, 7-, 8-, or 12-membered ring, gives rise to the corresponding silylbicyclo[n.3.0]alkanes 11-13. The cycloaddition of allyltriisopropylsilane (1k) and 1-acetyl-2-methylcycloalkenes 15 provides silylbicyclo[n.3.0]alkanes 16 with two contiguous quaternary carbon centers. The stereochemistry of the silylbicyclo[n.3.0]alkanes 11a-c and 14 is unambiguously determined by X-ray analysis and 13C NMR spectroscopy.
- Knoelker, Hans-Joachim,Foitzik, Norbert,Goesmann, Helmut,Graf, Regina,Jones, Peter G.,Wanzl, Guenter
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p. 538 - 551
(2007/10/03)
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- Antitumor cyclopentnaphthoquinone and cyclopentanthraquinone derivatives
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The present invention provides compounds having the structure: STR1 or having the structure: STR2 The present invention also provides a pharmaceutical compostion containing the compounds, methods of synthesizing the compounds, as well as methods of inhibi
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- TRANSFORMATIONS OF N-METHYL-4,5-DIHYDROISOXAZOLIUM METHYLSULPHATES
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Reactions of N-methyl-4,5-dihydroisoxazolium methylsulphates with: H2O, H2O2 or KMnO4, NaNO2, NEt3, NaCN, NaN3 yielded respectively: β-methylaminoxyketones, β-hydroxyketones, β-(N-nitroso)methylaminoxyketones, a mixture of N-methyl-2,5-dihydroisoxazole an
- Kwiatkowski, Stefan,Ostrowski, Stanislaw
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p. 259 - 270
(2007/10/02)
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- SYNTHESIS OF QUEEN SUBSTANCE VIA THREE CARBON HOMOLOGATION ROUTE
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The acetoxyaldehyde 9 prepared in five steps from methylcyclohexene 4 furnished the alkylidine succinic ester 12 when reacted with diethyl diethoxyphosphinylbutanedioate 11.The ester 12 was transformed to the half ester 17, which on oxidative decarboxylation (lead tetraacetate, cupric acetate) gave a 3:1 mixture of esters 18 and 2 which was converted to the Queen Substance 1.
- Dhokte, U. P.,Rao, A. S.
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p. 355 - 368
(2007/10/02)
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- Facile Synthesis of Allylic Nitro Compounds by N,N-dimethylethylenediamine-Catalyzed Condensation of Aliphatic and Alicyclic Ketones with Primary Nitroalkanes
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Aliphatic as well as alicyclic ketones condense with primary nitroalkanes in the presence of N,N-dimethylethylenediamine (1) to give allylic nitro compounds selectively in good to excellent yields without forming α-nitro olefins.Condensation of 2-alkanones and 2-methylcyclopentanone with nitromethane produces the products of thermodynamic control, while the product of kinetic control is obtained from 2-methylcyclohexanone.Propiophenone, an aromatic ketone, reacted with nitromethane in a way analogous to aliphatic ketones to give the corresponding allylic nitro product.A reaction mechanism to account for the exclusive formation of allylic nitro compounds is proposed.Some allylic nitro compounds thus obtained are converted into α,β-unsaturated aldehydes and ketones by treatment with sodium methoxide and then TiCl3 in buffered solution.
- Tamura, Rui,Sato, Masahiro,Oda, Daihei
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p. 4368 - 4375
(2007/10/02)
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- Process for production of α,β-unsaturated ketones
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A process for producing an α,β-unsaturated ketone of the general formula STR1 wherein R1 represents a hydrocarbon group, R2 represents an organic group bonded through a carbon-carbon bond, R3 and R4 represent a hydrogen atom or a hydrocarbon group, and R1, R2, R3 and R4 may be linear or may form a ring when taken together in arbitrary combinations, which comprises contacting an α-disubstituted-β-keto acid ester of the general formula STR2 wherein R1, R2, R3 and R4 are as defined, and R5, R6 and R7 represent a hydrogen atom or a hydrocarbon group, with a catalyst consisting essentially of (a) a compound of a platinum-group metal and (b) and α,ω-alkylenedi(disubstituted)phosphine.
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- A NEW SYNTHESIS OF α,β-UNSATURATED KETONES. ALLYLIC ALKYLATION OF 1-ISOCYANO-1-TOSYLALKENES
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Ketones (1) are homologated to enones 2 by alkylating (introduction of R3) the condensation products 4 (derived from 1 and tosylmethyl isocyanide), followed by acid catalyzed hydrolysis.
- Moskal, Janusz,Leusen, Albert M. van
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p. 2585 - 2588
(2007/10/02)
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- Vinyl Cations, 37. Rearrangement of Cyclic Homopropargyl Sulfonates to Condensed Cyclobutanones and Cyclopropyl Ketones
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Cyclic homopropargyl sulfonates 8 (tosylates, triflates, nonaflates, and damsylates) are prepared and solvolysed.The resulting rearrangement reactions are studied with respect to the properties of the solvents used, leaving groups, the substituent on the triple bond, and with respect to the ring size of the sulfonates 8.
- Hanack, Michael,Schuhmacher, Werner,Kunzmann, Erich
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p. 1467 - 1487
(2007/10/02)
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- Process for preparation of adjacently disubstituted ketones
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A novel 7-hydroxyprostaglandin E1, or a stereoisomer thereof, or a protected derivative thereof, having the following formula: STR1 wherein R8 represents H, CH3 or C2 H5, R9 represents H or CH3, R10 and R11 are identical or different, and each represents H, tetrahydropyranyl or t-butyldimethylsilyl. Also provided is a process for producing an adjacently disubstituted ketone including the above compounds, i.e. 7-oxoprostaglandin, etc. which comprises reacting an α,β-unsaturated carbonyl compound with a cuprous salt and an organolithium compound in an aprotic inert organic medium in the presence of trialkylphosphine, the amounts of said cuprous salt and said organolithium compound being substantially equimolar, and reacting the product with a protected acetal derivative of an organic carbonyl compound or an aldehyde in the presence of a Lewis acid, if necessary, followed by reacting the product with a proton donor.
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- ALUMINUM OXIDE CATALYZED ISOMERIZATION OF ACYLATED CYCLOALKENES
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A homologous series of cyclic olefins and their corresponding 1-methyl derivatives were acylated using acetic anhydride/zinc chloride system.The resulting mixtures were, after appropriate analysis, isomerized quantitatively to the conjugated enones by adsorption on neutral alumina.A detailed, general experimental procedure is given.
- Hudlicky, T.,Srnak, T.
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p. 3351 - 3354
(2007/10/02)
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- Oxydation anodique de β-cetocarboxylates en milieu aqueux ou hydroorganique. Application a la synthese de γ-dicetones, de cetones ethyleniques et de cetoamides
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A systematic study of the anodic oxidation of β-ketocarboxylate anions in aqueous or hydroorganic solvents allows to distinguish the factors directing this reaction.Thus, it is possible by the appropriate choice of reaction medium and structure of the starting ion to synthesize products such as γ diketones, ethylenic ketones and ketoamides.
- Chkir, Moncef,Lelandais, Daniel,Bacquet, Cathy
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p. 945 - 951
(2007/10/02)
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- Influence de la taille du cycle sur la substitution electrophile des cycloalkyltrimethylsilanes. Synthese de cycloalkyldimethylfluorosilanes
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Cycloalkyltrimethylsilanes, excepting cyclopropyl-, react with electrophiles by Si - Me bond splitting.Consequently silicon can be functionalized by this route.We also propose a new synthesis of cycloalkyldimethylfluoro(or chloro-)silanes.In the case of five or six member ring derivates, the observed results are interpreted by a mechanism involving initial abstraction of hydride ion from the silicon substrate.
- Grignon-Dubois, M.,Dunogues, J.,Calas, R.
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p. 291 - 295
(2007/10/02)
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- Malonate Anion Induced Favorskii-Type Rearrangement. Reaction of Cyclic α-Halo Ketones with Sodiomalonates
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The reaction of 2-chlorocyclohexanone (1b) with ethyl sodiomalonate in benzene at 0-25 deg C gave 6-bicyclohexan-6-ol (4c), the Favorskii-type intermediate, in 49percent yield, in place of the substitution product ethyl C-(2-oxocyclohexyl)malonate (3).Derivatives of bicycloheptan-7-ol (4a,b) and those of bicyclohexan-6-ol (4d,e) were also obtained in good yields by similar means.Compound 4c was transformed into 3 readily by heating with 0.05 equiv of NaH in benzene.The hydrolysis of 4a-d with 0.2 N NaOH followed by pyrolysis at 110-120 deg C gave the ring-contracted β-keto esters 9a-d.Pyrolysis after the hydrolysis with 2N NaOH gave the corresponding ketones 11a-d in good yields.Oxidation of 4c with CrO3 and HClO4 afforded ethyl C-(2-hydroxycyclopentanecarbonyl)malonate (14) in 45 percent yield.Treatment of 4c with Br2 gave ethyl C-(1-bromocyclopentanecarbonyl)malonate (18) in 64 percent yield.
- Sakai, Takashi,Amano, Eiichiro,Kawabata, Akifumi,Takeda, Akira
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