- Catalysis-based and protecting-group-free total syntheses of the marine oxylipins hybridalactone and the ecklonialactones A, B, and C
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Concise and protecting-group-free total syntheses of the marine oxylipins hybridalactone (1) and three members of the ecklonialactone family (2-4) were developed. They deliver these targets in optically pure form in 14 or 13 steps, respectively, in the longest linear sequence; five of these steps are metal-catalyzed and four others are metal-mediated. The route to either 1 or 2-4 diverges from the common building block 22, which is accessible in 7 steps from 2[5H]furanone by recourse to a rhodium-catalyzed asymmetric 1,4-addition reaction controlled by the carvone-derived diene ligand 35 and a ring-closing alkene metathesis (RCM) catalyzed by the ruthenium indenylidene complex 17 as the key operations. Alternatively, 22 can be made in 10 steps from furfural via a diastereoselective three-component coupling process. The further elaboration of 22 into hybridalactone as the structurally most complex target with seven contiguous chiral centers was based upon a sequence of cyclopropanation followed by a vanadium-catalyzed epoxidation, both of which were directed by the same free hydroxy group at C15. The macrocyclic scaffold was annulated to the headgroup by means of a ring-closing alkyne metathesis reaction (RCAM). In response to the unusually high propensity of the oxirane of the targeted oxylipins for ring opening, this transformation had to be performed with complexes of the type [(Ar3SiO)4Mo≡CPh] [K·OEt2] (43), which represent a new generation of exceedingly tolerant yet remarkably efficient catalysts. Their ancillary triarylsilanolate ligands temper the Lewis acidity of the molybdenum center but are not sufficiently nucleophilic to engage in the opening of the fragile epoxide ring. A final semireduction of the cycloalkyne formed in the RCAM step to the required (Z)-alkene completed the total synthesis of (-)-1. The fact that the route from the common fragment 22 to the ecklonialactones could follow a similar logic showcased the flexibility inherent to the chosen approach.
- Hickmann, Volker,Kondoh, Azusa,Gabor, Barbara,Alcarazo, Manuel,Fuerstner, Alois
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supporting information; experimental part
p. 13471 - 13480
(2011/10/10)
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- Enantioselective intramolecular hydroarylation of alkenes via directed C-H bond activation
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(Chemical Equation Presented) Highly enantioselective catalytic intramolecular ortho-alkylation of aromatic imines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using [RhCl(coe)2]2 and chiral phosphoramidite ligands. Cyclization of substrates containing 1,1- and 1,2-disubstituted as well as trisubstituted alkenes were achieved with enantioselectivities >90% ee for each substrate class. Cyclization of substrates with Z-alkene isomers proceeded much more efficiently than substrates with E-alkene isomers. This further enabled the highly stereoselective intramolecular alkylation of certain substrates containing Z/E-alkene mixtures via a Rh-catalyzed alkene isomerization with preferential cyclization of the Z-isomer.
- Harada, Hitoshi,Thalji, Reema K.,Bergman, Robert G.,Ellman, Jonathan A.
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p. 6772 - 6779
(2008/12/22)
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- Synthesis of enamides from aldehydes and amides
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A range of double unsaturated amides (15, 19, and 21), obtained by cross-coupling reactions was reacted with aldehydes to hemiaminals. Heating the hemiaminals in the presence of Ac2O and pyridine affected clean conversion to the corresponding enamides, such as 42, 45, and 47. Alternatively, N,S-acetals were prepared which were oxidized to the sulfones. Treatment with base also gave the enamides, favoring the cis-isomer. However, this method is less general. Application of these methods led to the natural products lansiumamide-A (30_cis), lansiumamide-I (31) and lansiumamide-B (32).
- Bayer, Alexander,Maier, Martin E.
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p. 6665 - 6677
(2007/10/03)
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- Pheromone synthesis; CXXXIII. Synthesis of both the enantiomers of (3Z,9Z)-cis-6,7-epoxy-3,9-nonadecadiene, a pheromone component of Erannis defoliaria
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Both the enantiomers of (3Z,9Z-cis-6,7-epoxy-3,9-nonadecadiene, a pheromone component of Erannis defoliaria, were synthesized using the Sharpless asymmetric epoxidation as the key step.
- Mori,Brevet
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p. 1125 - 1129
(2007/10/02)
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- Sila-pheromones: Silicon analogues of the female sex pheromone of the processionary moth Thaumetopoea pityocampa
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The 15- and 10-dimethylsila-analogues of (Z)-13-hexadecen-11-ynyl acetate, the main component of the female sex pheromone of the processionary moth Thaumetopoea pityocampa, were synthesized to evaluate the influence of the silicon atom on the biological activity.
- Arsequell, Gemma,Camps, Francisco,Fabrias, Gemma,Guerrero, Angel
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p. 2739 - 2742
(2007/10/02)
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- Une synthese courte et stereoselective de l'Acetoxy-1 hexadecane-13 (Z)yne-11 : Principal constituant de la secretion pheromonale produite par la femelle vierge de la Processionnaire du pin Theumetopoes pityocampa (Danis et Schiff.) (Lepidoptera notodontides).
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Resume : Une synthese courte et stereoselective de la pheromone sexuelle de la Processionnaire du pin : Thaumatopoes pityocamps (Denis et Schiff.) a ete realisee.Cette synthese utilise dans son etape finale une reaction de couplage d'un acetate ω-acetylenique sur un halogenure vinylique dans le benzene en presence de quantites catalytiques de tetrakis(triphenylphosphine)palladium et d'iodure cuivreux.
- Michelot, Didier,Guerrero, Angel,Ratovelomanana, Victorin
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p. 1043 - 1051
(2007/10/02)
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