- Preparation of 3(S)-Ethyl-Heptanoic Acid from (S)-Limonene A Chiron Approach
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Optically active 3-ethyl-heptanoic acid is readily synthesized from limonene.
- Chiu, Charles K.-F.
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- What Limits the Molecular Weight and Controlled Synthesis of Poly(3-alkyltellurophene)s?
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Polytellurophenes are an emerging class of conjugated polymers; however, their controlled polymerization leading to high molecular weight materials has been a major challenge. Here we present a systematic investigation of the synthesis of poly(3-alkyltellurophene)s using the catalyst transfer polycondensation methodology. Learning that previous syntheses were limited by both polymerization reaction kinetics and polymer solubility, we design new tellurophene monomers to overcome these limitations. Controlled polymerization behavior up to Mn = 25 kDa, chain extension, block copolymerization, external initiation, and well-defined end groups are demonstrated for poly(3-alkyltellurophene)s with appropriately designed side chains. We clarify the role that side-chain branching point plays on polymerization kinetics and optical properties for these prototypical regioregular polymers. In addition, the effect that monomer addition sequence has on well-defined tellurophene-thiophene block copolymers was studied. The controlled polymerization of tellurophene should provide access to more complex polymeric architectures involving these and other conjugated monomers. The methods used to optimize the polymerization of alkyltellurophenes should be applicable to other monomers that have been challenging to synthesize in a controlled manner.
- Ye, Shuyang,Steube, Marvin,Carrera, Elisa I.,Seferos, Dwight S.
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- (S,S)-(+)-pseudoephedrine as chiral auxiliary in asymmetric conjugate addition and tandem conjugate addition/α-alkylation reactions
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(Chemical Equation Presented) Organolithium reagents undergo highly regio- and diastereoselective 1,4-addition to (S,S)-(+)-pseudoephedrine enamides furnishing the corresponding β-alkyl-substituted adducts in excellent yields and diastereoselectivities. In addition, the intermediate lithium enolates generated after the conjugate addition step undergo a highly diastereoselective alkylation reaction, furnishing α,β-dialkyl- substituted amides in high yields. The obtained adducts have been converted into chiral nonracemic β-alkyl- and α,β-dialkyl-substituted carboxylic acids and γ-alkyl- and β,γ-dialkyl-substituted alcohols using very simple and high-yielding procedures.
- Reyes, Efraim,Vicario, Jose L.,Carrillo, Luisa,Badia, Dolores,Uria, Uxue,Iza, Ainara
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p. 7763 - 7772
(2007/10/03)
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- Enantioselective carbometalation of cinnamyl derivatives: New access to chiral disubstituted cyclopropanes - Configurational stability of benzylic organozinc halides
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A stoichiometric or catalytic amount of (-)-sparteine can serve asa promoter for the enantioselective carbolithiation of cinnamyl derivatives by primary and secondary organolithium compounds. The enantiofacial choice of the addition reaction is dependent on the stereochemistry of the initial double bond. The resulting benzylic organolithium compounds can be derivatized to a linear phenylated chain that bears two contiguous stereogenic centers with given configurations. The use of the dimethyl acetal of the (E)-cinnamyl alcohol allows the highest enantioselective carbolithiation and by simply warming the reaction mixture to room temperature, the resulting benzylic organo-lithium intermediate undergoes a 1,3-elimination to give the chiral disubstituted cyclopropane in high enantiomeric excess (90-95% ee). Another significant finding is the observation that the Li-Zn transmetalation in a benzylic species occurs with inversion of configuration, and the corresponding acyclic benzylic zinc halides have observable configurational stability at - 30°C.
- Norsikian, Stephanie,Marek, Ilan,Klein, Sophie,Poisson, Jean F.,Normant, Jean F.
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p. 2055 - 2068
(2007/10/03)
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- Enantioselective carbolithiation of β-alkylated styrene
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Stoichiometric or catalytic amounts of (-) sparteine serve as promoter for enantioselective carbolithiation of β-alkylated, non functionalized styrene.
- Norsikian, Stephanie,Marek, Ilane,Normant, Jean-F.
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p. 7523 - 7526
(2007/10/03)
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