- Size-Exclusion Borane-Catalyzed Domino 1,3-Allylic/Reductive Ireland–Claisen Rearrangements: Impact of the Electronic and Structural Parameters on the 1,3-Allylic Shift Aptitude
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The reductive Ireland–Claisen rearrangement through borane-mediated hydrosilylation is reported. The method employs a borane catalyst with a special structural design and affords access to synthetically relevant products with high diastereoselectivity. Depending on electronic and structural parameters, the reaction can be coupled with a 1,3-allylic shift, thus the valence isomer of the Ireland–Claisen product is formed.
- Fegyverneki, Dániel,Kolozsvári, Natália,Molnár, Dániel,Egyed, Orsolya,Holczbauer, Tamás,Soós, Tibor
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supporting information
p. 2179 - 2183
(2019/01/04)
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- Highly enantioselective synthesis of 3-substituted furanones by palladium-catalyzed kinetic resolution of unsymmetrical allyl acetates
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Resolving the issue: A near-perfect Pd-catalyzed kinetic resolution of 1,3-disubstituted unsymmetrical allylic acetates uses silyl enol ethers as nucleophiles to access the important 3-substituted-furanone scaffold (see scheme; DACH=diaminocyclohexyl, dba=dibenzylideneacetone). The reaction proceeds under mild conditions and provides the desired products with excellent chemo-, regio-, and enantioselectivity. Copyright
- Mao, Bin,Ji, Yining,Fananas-Mastral, Martin,Caroli, Giuseppe,Meetsma, Auke,Feringa, Ben L.
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supporting information; experimental part
p. 3168 - 3173
(2012/05/05)
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- Stereoselective synthesis of furans by the Pd-catalyzed Oshima-Utimoto reaction
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(Chemical Equation Presented) The Pd-catalyzed coupling of acyclic allylic alcohols with vinyl ethers was examined and found to proceed with 2.5-10 mol % of catalyst and to provide cyclic acetals with good stereoselection. The reaction is tolerant of a number of functional groups and can be used to generate quaternary centers in a stereoselective fashion.
- Evans, Michael A.,Morken, James P.
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p. 3367 - 3370
(2007/10/03)
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- Molybdenum(0) and tungsten(0) catalysts with enhanced reactivity for allylic substitution: Regioselectivity and solvent effects
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The binuclear Mo(II) and W(II) complexes 28a,b and 29a,b have been developed as pre-catalysts for allylic substitution with β-dicarbonyl nucleophiles. These complexes are reduced in situ to Mo(0) and W(0) catalytic species 30a,b and 31a,b by excess of NaH, employed to generate sodiomalonate nucleophiles, or by DIBAL-H. 1,3-Dioxolane and 1,4-dioxane, when used as solvents, substantially accelerate the reaction. These new catalysts exhibit "traditional" Mo regiochemistry, i.e., the nucleophilic attack occurring preferentially at the more substituted carbon (5 → 9; 37 → 38), unless an additional factor, such as further coordination to another moiety of the allylic electrophile takes part (41), as in the case of the geranyl-type substrates (32 or 33 → 36).
- Malkov,Baxendale,Mansfield,Kocovsky
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p. 1234 - 1240
(2007/10/03)
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- Rhodium promoted isomerisation of allylic alkoxides: A new method for enolate anion formation
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Transition metal mediated isomerisation of allylic alkoxides is presented as a new method for enolate anion generation. The scope and limitations of enolate formation with the catalysts [Rh(dppe)(THF)2]+ClO4- and (Ph3P)3RhCl are explored and the synthetic potential of the methodology demonstrated in the stereoselective formation and reactions of certain ketone and aldehyde enolates.
- Gazzard, Lewis J.,Motherwell, William B.,Sandham, David A.
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p. 979 - 993
(2007/10/03)
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- A Regioselective and Stereospecific Synthesis of Allylsilanes from Secondary Allylic Alcohol Derivatives
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Primary and secondary allylic acetates and benzoates react with the dimethyl(phenyl)silyl-cuprate reagent to give allylsilanes, provided that the THF in which the cuprate is prepared is diluted with ether before addition of the allylic ester.The reaction is reasonably regioselective in some cases: (i) when the allylic system is more-substituted at one end than the other, as in the reactions 4->5 and 9->10; (ii) when the steric hindrance at one end is neopentyl-like, as in the reactions 15->16; and (iii) when the disubstituted double bond has the Z configuration, as in th e reactions Z-19->E-21 or, better, because the silyl group is becoming attached to the less-sterically hindered end of the allylic system, Z-20->E-22.The regioselectivity is better if a phenyl carbamate is used in place of the ester, and a three-step protocol assembling the mixed cuprate on the leaving group is used, as in the reactions 23->24 and E- or Z-29->E-21, or, best of all, because the silyl group is again becoming attached to the less-sterically hindered end of the allylic system, E- or Z-30->E-22.This sequence works well to move the silyl group onto the more substituted end of an allyl system, but only when the move is from a secondary allylic carbamate to a tertiary allylsilane, as in the reaction 38->39.Allyl(trimethyl)silanes can be made using alkyl- or aryl-cuprates on trimethylsilyl-containing allylic esters and carbamates, as in the reactions 40->41, and 43->44.The reaction of the silyl-cuprate with allylic esters and the three-step sequence with the allylic carbamates are stereochemically complementary, the former being stereospecifically anti and the latter stereospecifically syn.Homochiral allylsilanes can be ma de by these methods with high levels of stereospecificity, as shown by the synthesis of the allylsilanes 54, 58 and 59.
- Fleming, Ian,Higgins, Dick,Lawrence, Nicholas J.,Thomas, Andrew P.
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p. 3331 - 3350
(2007/10/02)
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- Stereo- and Regiochemistry in Palladium-Catalyzed Nucleophilic Substitution of Optically Active (E)- and (Z)-Allyl Acetates
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Optically acive (E)- and (Z)-allyl acetates, 3-acetoxy-1-phenyl-1-butene (1) and its regioisomer, 1-acetoxy-1-phenyl-3-butene (2), were allowed to react with sodium dimethyl malonate, sodium acetylacetonate, and sodium methyl acetoacetate in the presence of a palladium catalyst.The reaction of (E)-acetates proceeded with retention of configuration and that of (Z)-acetates proceeded with inversion accompanied by geometrical isomerization from Z to E.The stereochemistry observed in the reaction with phenylzinc bromide was opposite to that with the soft nucleophiles.
- Hayashi, Tamio,Yamamoto, Akihiro,Hagihara, Toshiya
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p. 723 - 727
(2007/10/02)
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- Alkylation of Allylic Derivatives. 3. The Regiochemistry of Alkylation of the Isomeric trans-α,γ-Methylphenylallyl Acetates with Lithium Dialkyleuprates
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Alkylation of the isomeric trans-α,γ-methylphenylallyl acetates (1-OAc and 2-OAc) with lithium dimethylcuprate or di-n-butylcuprate is regioselective but not regiospecific.Both isomers give essentially the same product mixture which contains 95percent of the trans conjugated alkylation product (3).The starting acetates do not rearrange under the conditions for these reactions.These results show that the isomeric acetate give the same product-forming intermediate(s).Presumably the key intermediate that is common to the two isomers is a ?-allyl copper(III).
- Goering, Harlan N.,Seitz, Earl P.,Tseng, Chung Chyi
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p. 5304 - 5308
(2007/10/02)
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