- A de novo asymmetric approach to achiral deoxy-melodorinol analogues
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A short and highly efficient route to deoxy-Melodorinol analogues has been developed. The key to the overall transformation is the use of an enantioselective Sharpless asymmetric dihydroxylation of an (Z,E)-dienoate to control the regioselectivity of the dihydroxylation reaction and a Mitsunobu elimination reaction to control the E-stereochemistry of the,δ-double bond. The highly efficient synthesis stereoselectively prepared four analogues in 3 steps from 4-substituted crotonaldehydes.
- Ahmed, Md. Moinuddin,Akhmedov, Novruz G.,Cui, Hu,Friedrich, Dirk,O'Doherty, George A.
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p. 223 - 233
(2008/02/02)
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- Highly cis-selective Horner-Wadsworth-Emmons (HWE) reaction of methyl bis(2,4-difluorophenyl) phosphonoacetate
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Of the previously reported Homer-Wadsworth-Emmons (HWE) reaction, the olefination of methyl bis(2,4-difluorophenyl)phosphonoacetate (1a) with various aldehydes gave unsaturated esters in the highest cis-selectivity.
- Kokin, Keisuke,Motoyoshiya, Jiro,Hayashi, Sadao,Aoyama, Hiromu
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p. 2387 - 2392
(2007/10/03)
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- Vinylcyclobutane-Cyclohexane Rearrangements: Zwitterions as Discrete Intermediates
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Donor-acceptor-substituted vinylcyclobutanes 1 rearrange to cyclohexenes 2 at temperatures between 20 and 195 deg C.In solvents of low polarity, cycloreversion competes with ring enlargement.Under acidic conditions, addition of nucleophiles to vinylcyclobutanes 1 with ring opening is observed.Stereospecificity of rearrangement and cycloreversion are functions of temperature, solvent polarity and acid catalysis.Strong dependence on solvent polarity is found for the rates of both reactions.The mechanisms of the thermally induced and acid-catalyzed reactions are discussed on the basis of stereospecificity, kinetic parameters and trapping of intermediates.Two structurally different zwitterions 13 and 14 are proposed as intermediates, one of which is responsible for rearrangement, the other for diastereomerization and cycloreversion.
- Gruseck, Ursula,Heuschmann, Manfred
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p. 1911 - 1926
(2007/10/02)
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- An Efficient One-Pot Preparation of 2,4-Pentadienoic Esters from α,β-Unsaturated Aldehydes
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α,β-Unsaturated aldehydes react with monoalkyl malonates in pyridine with a catalytic amount of dimethylaminopyridine (DMAP) in a regio- and stereoselective process to yield almost exclusively 2,4-pentadienoic esters with essentially (and in many cases exclusively) the 2E-stereochemistry.
- Rodriguez, J.,Waegell, B.
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p. 534 - 535
(2007/10/02)
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- Stereoselective Synthesis of (2E,4E)- and (2Z,4E)-2,4-Alkadienoates by the Ester Enolate Claisen Rearrangement of (E)-1-Alkyl-3-trimethylsilyl-2-propenyl Glycolates Followed by the Peterson Reaction
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The ester enolate Claisen rearrangement of (E)-1-alkyl-3-trimethylsilyl-2-propenyl glycolates gave (E)-erythro-2-hydroxy-3-trimethylsilyl-4-alkenoates with high diastereoselectivity, which were stereoselectively converted into (2E,4E)- and (2Z,4E)-2,4-alkadienoates by the Peterson reaction.
- Sato, Toshio,Tsunekawa, Hiroshi,Kohama, Hiromasa,Fujisawa, Tamotsu
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p. 1553 - 1556
(2007/10/02)
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- SYNTHESE STEREOSELECTIVE D'ESTERS α,β-ETHYLENIQUES α-METHYLES Z OU E PAR LA REACTION DE WITTIG-HORNER A PARTIR DE PHOSPHONATES OU D'OXYDES DE PHOSPHINE
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The reaction of α-branched aldehydes with diethyl 1-carbomethoxyethyl phosphonate 1b in THF/nBuLi at low temperature leads stereoselectively to Z α-methyl α,β-unsaturated esters.From a linear aldehyde, the reaction is less stereoselective, while from α,β-unsaturated ones, the E isomers are predominantly formed in good yields.From diphenyl 1-carbomethoxyethyl phosphine oxide 2b, E α-methyl α,β-unsaturated esters are stereoselectively formed either in DMF/tBuOK or in phase transfer conditions, whatever the starting aldehyde is, also in good yields.This reagent can thus advantageously replace the corresponding P-ylid.In all cases, the reaction conditions are determined so that by-products formation is minimized.
- Etemad-Moghadam, Guita,Seyden-Penne, Jacqueline
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p. 5153 - 5166
(2007/10/02)
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