- Two Ene-Yne Metathesis Approaches to the Total Synthesis of Amphidinolide P
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The total synthesis of amphidinolide P was achieved through two different ene-yne metathesis approaches. In each approach, the metathesis step was performed at late stages in the synthesis with all other functionality present. By forging two successful pa
- Jecs, Edgars,Diver, Steven T.
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- Gold-Catalyzed Asymmetric Thioallylation of Propiolates via Charge-Induced Thio-Claisen Rearrangement
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A gold(I)-catalyzed enantioselective thioallylation of propiolates with allyl sulfides is described. The key mechanistic element is a sulfonium-induced Claisen rearrangement which helps minimize the allyl dissociation and render higher enantioselectivity. This protocol features remarkable scope of the allyl moiety, allowing enantiocontrolled synthesis of all-carbon quaternary centers, and exhibits exceptional functional group compatibility with many Lewis bases and π-bonds. This intermolecular variant of Claisen rearrangement forges both C-S and C-C bonds concomitantly, providing efficient access to interesting optically active organosulfur compounds which can be transformed further through the vinyl sulfide as a functional handle. The rate of the reaction was zeroth order with respect to allyl sulfides, which suggested a reversible inhibition, providing a resting state for the catalyst. The Hammett plot displayed a correlation with σp values, suggesting a turnover-limiting sigmatropic rearrangement where decreased electron-density on sulfur accelerated the rearrangement.
- Kim, Hanbyul,Jang, Jiwon,Shin, Seunghoon
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supporting information
p. 20788 - 20795
(2020/11/27)
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- Chemistry of Dioxenium Cations. Synthetic and Mechanistic Studies on the Stereocontrolled Formation of Tetrahydropyrans from Homoallylic Alcohols and Ortho Esters
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Despite their long history, dioxenium cations are underutilized reactive synthetic intermediates.It was found that ortho esters and homoallylic alcohols in the presence of Lewis acids provide 4-heterosubstituted pyranosides in a stereoselective manner.The
- Perron-Sierra, Francoise,Promo, Michele A.,Martin, Van A.,Albizati, Kim F.
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p. 6188 - 6199
(2007/10/02)
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- HIGHLY ENANTIOSELECTIVE ISOMERIZATION OF PROCHIRAL ALLYLAMINES CATALYZED BY CHIRAL DIPHOSPHINE RHODIUM(I) COMPLEXES. PREPARATION OF OPTICALLY ACTIVE ENAMINES
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Rh(I) complexes of types ClO4 and n>ClO4 (diphosphine = cis-chelating tertiary diphosphine; diene = 1,5-cyclooctadiene or norbornadiene; S = solvent) were found to be effective catalists for allylic hydrogen migration of tertiary and secondary allylamines to give the corresponding (E)-enamines and imines, respectively.Studies on diphosphine ligands with respect to the catalytic activity and product selectivity led to the discovery of a fully aryl-substituted diphosphine, BINAP , which produces very active Rh(I) complex catalysts.With ClO4 (COD = 1,5-cyclooctadiene) or n>ClO4 as catalyst, (Z)-(diethylnerylamine, 1) or (E)-N,N-diethyl-3,7-dimethyl-2,6-octadienylamine (diethylgeranylamine, 2) was isomerized into the racemic (E)-enamine (E)-N,N-diethyl-3,7dimethyl-1,6-octadienylamine (citronellenamine, 3) with a chemical selectivity of over 95percent, the 6-double bond being retained intact.A variety of substituted allylamines serves as the substrate, e.g., (E)-N,N-dimethyl-2-butenylamine, N,N-dimethyl-2-methyl-2-propenylamine, N,N-dimethyl-3-methyl-2-butenylamine, N,N-dimethyl-3-phenyl-2-butenylamine.Asymmetric isomerization of prochiral allylamines producing optically active enamines or imines can be effected with cationic Rh(I) complexes of various chiral diphosphine ligands such as (2R,3R)-DIOP and others.The ligand that gives the highest optical yield was (+)- or (-)-BINAP.Virtually perfect enantioselectivity (95-99percent ee) was achieved with + for the isomerization of 1 or 2 into the optically active (E)-enamine (3).A clear stereochemical correlation was established between the olefin geometry (E or Z) of substrates, the configuration of the chiral diphosphines (R or S), and the chiral carbon configuration of the product enamines (R or S).The present catalytic system thus provides a convenient and practical access to optically active aldehydes.For example, optically pure natural citronellal can be produced either from nerylamine with the Rh(I)-(+)-BINAP catalyst or from geranylamine with the Rh(I)-(-)-BINAP complex catalyst.
- Tani, Kazuhide,Yamagata, Tsuneaki,Akutagawa, Susumu,Kumobayashi, Hidenori,Taketomi, Takanao,et al.
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p. 5208 - 5217
(2007/10/02)
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- Copper(I)-Mediated Synthesis of cis-Isoprenoids. Models for Natural Rubber
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Two copper(I)-mediated routes for the preparation of all-cis-2,6,10-trimethyl-2,6,10-dodecatriene are investigated.Reaction of the Grignard reagent derived from 1-bromo-4-methylpent-3-ene with CuBr, and then with excess propyne, gave a vinylcopper intermediate which could be alkylated with 1-iodo-3-methylpent-3-ene, to afford the required triene stereospecifically cis- in 28percent yield.Iodination of the same intermediate and subsequent conversion to 1-bromo-4,8-dimethyl-3,7-nonadiene is shown to occur with retention of configuration, so allowing the iterative construction of cis-isoprenoids.This vinylcopper-based route is shown to be also applicable to the synthesis of larger cis-isoprenoids.In contrast, the CuI-modified coupling reaction of the Grignard reagent from 1-chloro-2-methylbut-2-ene with neryl chloride gave a mixture of triene isomers.
- Parr, William J. E.
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p. 4101 - 4130
(2007/10/02)
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- The Influence of Chain-branching on the Steric Outcome of Some Olefin-forming Reactions
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When applied to the construction of internal disubstituted double bonds in compounds such as pentadec-7-ene and 2,6,11,15-tetramethylhexadeca-2,6,8,10,14-pentaene (5), the reductive elimination of vicinal benzoyloxy-sulphones gives products with a trans:cis ratio of ca. 4:1.When applied to the construction of disubstituted olefins in which branching occurs adjacent to the newly formed double bond, much higher trans-stereoselectivity is observed, e.g. for 5-ethyl-2-methylhept-3-ene (21) and 3,6-dimethylocta-2,4,6-triene (25) it is at least 98percent.A similar effect of chain-branching is also observed in some Wittig and Horner reactions using primary allylic phosphorus derivatives.When a Z-allylic sulphone is used as the starting material in the benzoyloxy-sulphone method, the original Z-geometry is preserved in the product; (Z)-2-methylbut-2-enyl p-tolyl sulphone and tiglic aldehyde give almost exclusively (2E,4E,6Z)-3,6-dimethylocta-2,4,6-triene (27).
- Kocienski, Philip J.,Lythgoe, Basil,Waterhouse, Ian
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p. 1045 - 1050
(2007/10/02)
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