- Highly chemoselective lithium metal reductions of benzaldehyde bis(2-methoxyethyl) acetals
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Naphthalene-catalysed reductions of PhCH(OR)2 (R = Me, CH2CH2OMe) acetals by lithium metal, followed by reactions with electrophiles (H+, TMSCl, nBuBr, CH2=CHCH2Br), proceed with high chemoselectivity when the reductions are carried out at -90 °C especially for R = CH2CH2OMe. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany 2002.
- Von Schrader, Thomas,Woodward, Simon
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p. 3833 - 3836
(2007/10/03)
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- Asymmetric nucleophilic substitution of acetals
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Benzaldehyde dimethylacetal (1) and 2-aryl-1,3-dioxolanes 5 react with organolithium reagents 2 in the presence of chiral ligands such as sparteine (3), 1-alkoxy-2-aminoethanes, or 1,2-dialkoxyethanes and BF3 to afford monosubstitution products in high yields and in up to 81% enantiomeric excess. The enantioselectivity is strongly influenced by steric effects in the acetal and in the reagent. The highest ee was achieved with 2-(2-isopropyl)-1,3-dioxolane (5c) on treatment with 2-ethylphenyllithium (2i) in the presence of sparteine. The approach was applied to the synthesis of enantioenriched (S)-(-)-neobenodine (17) with 49% ee.
- Mueller, Paul,Nury, Patrice,Bernardinelli, Gerald
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p. 4137 - 4147
(2007/10/03)
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- Metalation of arylmethyl alkyl ethers
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Arylmethyl alkyl ethers 1a-11 were metallated with n-BuLi or sec-BuLi in THF at different temperatures, affording α-alkoxy-substituted arylmethyllithium derivatives. At low temperature, the organometallics derived from methyl and isopropyl ethers are suff
- Azzena, Ugo,Pilo, Luciano,Sechi, Alessandra
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p. 12389 - 12398
(2007/10/03)
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- Synthesis of Functionalized Heteroaromatics: Application to Formal Total Synthesis of Camptothecin
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The formal total synthesis of camptothecin was achieved via two types of lithiation reactions of pyridine derivatives and a Pd-catalyzed carbonylation of pyridylmethyl methanesulfonates.
- Murata, Naoko,Sugihara, Takumichi,Kondo, Yoshinori,Sakamoto, Takao
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p. 298 - 300
(2007/10/03)
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- Metalation of Arylmethyl Methyl Ethers and Connection with Their Reductive Electrophilic Substitution
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Stable α-methoxy arylmethyl carbanions can be generated by metalation of arylmethyl methyl ethers, 1, with n-BuLi in THF at -40 degC, avoiding Wittig rearrengement to the corresponding alkoxides 2.Reaction of these carbanions with various electrophiles afforded the expected products 3 in satisfactory yields.Connection between the metalation procedure and the reductive electrophilic substitution of arylmethyl methyl ethers allowed the transformation of compounds 1 into 2-arylpropanoic acids, 5.
- Azzena, Ugo,Demartis, Salvatore,Fiori, Maria Giovanna,Melloni, Giovanni,Pisano, Luisa
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p. 5641 - 5644
(2007/10/02)
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- Single and double reductive cleavage of C-O bonds of aromatic dimethyl acetals and ketals: Generation of benzylic mono- and dicarbanions
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The reductive cleavage of aromatic dimethyl acetals and ketals, 1, with Li metal in THF at low temperature allows the generation of stable α-alkoxy-α-arylsubstituted carbanions, avoiding the Wittig rearrangement. Reaction of these carbanions with various electrophiles afforded the expected products 2. Further in situ reaction of compounds 2 afforded the products of reductive electrophilic disubstitution, 3.
- Azzena,Melloni,Pisano,Sechi
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p. 6759 - 6762
(2007/10/02)
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- Photochemistry of Phenyl Alkyl Ketones in the Presence of Triphenylphosphine
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Photolysis of butyrophenone, valerophenone, γ-methylvalerophenone, and acetophenone in methanol in the presence of triphenylphosphine gave triphenylphosphine oxide and 1-phenyl-1-methoxyalkanes in addition to the expected Norrish type II products.Kinetic studies of these photoreactions by steady-state measurements show that triplet-state ketones are quenched by Ph3P but that the corresponding biradicals do not interact with Ph3P.
- Chow, Yuan L.,Marciniak, Bronislaw
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p. 2910 - 2914
(2007/10/02)
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- Benzylic Substitution of Benzyl Methyl Ether
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Treatment of benzyl methyl ether with n-butyl-lithium-tetramethylenediamine in hexane gave benzylic-lithiation, without ortho-lithiation or a Wittig type rearrangement.The benzylic-lithiated benzyl methyl ether was then allowed to react with benzophenone,
- Yeh, Ming Kuo
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p. 1652 - 1653
(2007/10/02)
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