Phasentransferkatalysierte Wittig‐Reaktionen ohne Basenzusatz
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Abstract:
Basefree Wittig Reactions with Phase Transfer Catalyts Ketones like trifluoroacetyl compounds — giving the haloform reaction in basic solutions — are able to react with mono or bis phosphonium fluorides without bases via Wittig reactions with very good yields. The phosphonium fluorides are prepared very easily from other phosphonium halides under phase transfer catalysis of crown ethers. The ratio of the stereoisomeric alkenes in the product and the spectra of the trans ‐ respectively trans‐trans alkenes are given.Keywords:
Wittig reaction
Phosphonium
Ylide
The silicon congeners of well-known phosphonium ylides have been considered only as short-lived reactive intermediates. We successfully synthesized a remarkably stable phosphonium sila-ylide. Its X-ray structure reveals a long Si-P bond and a strongly pyramidalized silicon center, indicating a very weak P-Si pi interaction. In addition, it exhibits an alpha,beta-ambiphilic character with a nucleophilic silicon center, similar to its carbon-congener phosphonium ylides. This property of the phosphonium sila-ylide allows its use as a sila-Wittig reagent with carbonyl derivatives.
Phosphonium
Ylide
Wittig reaction
Reactivity
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Phosphonium
Ylide
Wittig reaction
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Phosphonium
Wittig reaction
Ylide
Organic Synthesis
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Abstract ω-Azolylalkyltriphenylphosphonium bromides (5) were readily prepared from corresponding ω-bromo phosphonium salts (4) and azoles. The Wittig reactions of (5) with aromatic aldehydes were studied and 26 ω-azolyl alkenes were obtained. The reaction showed E-stereoselectivity.
Wittig reaction
Phosphonium
Phosphonium salt
Ylide
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Abstract The phase transfer catalyzed (PTC) Wittig reaction has the advantage of not requiring additional catalyst due to the catalytic property of phosphonium salt itself. This report presents the studies on such a reaction of diphenyl-, di-alkyl- and methyl-2-butenyl phosphonium ylids which are produced in situ from the corresponding phosphonium salts.
Wittig reaction
Phosphonium
Phosphonium salt
Phase-transfer catalyst
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Reaction of iodo Wittig ylide 1 with aldehyde 2 affords moderate yields of cis epoxides 6a and 7a, in addition to the expected olefin 3. A mechanism is proposed to account for both the high Z selectivity and the modest yield of olefin observed with this reagent.
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Ylide
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A series of α-sulfinyl phosphonium ylides have been obtained in the reaction of phosphonium mono- and diylides with sulfinic acid esters. The use of (−)-(S)-menthyl p-toluenesulfinate in this reaction afforded the corresponding (S)-((p-tolylsulfinyl)methyl)triphenylphosphonium ylide. The Wittig reaction of these ylides with saturated and unsaturated aldehydes resulted in the formation of racemic and optically active (+)-(R)-vinyl and dienyl sulfoxides with the E-geometry. The synthesis of (+)-(R)-((p-tolylsulfinyl)methyl)triphenylphosphonium iodide as a precursor of the optically active ylide has also been described.
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Wittig reaction
Phosphonium
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Abstract Schmidbaur's group have extensively investigated1 the coordination properties of phosphonium 1,3-ylide-anions (1) in organometallic chemistry and more recently Cristau2 has reported the potential usefulness of these compounds in synthetic organic chemistry. There have been a few studies3 of specific phosphonium 1,1-ylide-anions (2), however their only use in the Wittig reaction appears to be that of (2a).4 We have set out to study the stereochemistry and mechanism of Wittig reactions of (1) and (2) and to carry out some preliminary investigations on the arsenic analogues (3).
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Ylide
Wittig reaction
Phosphonium salt
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Abstract Stable Wittig reagents effectively reacted with episulfides to afford dialkyl fumarates and dialkyl maleates in good yields. The reaction probably occurred via attack of the ylide carbanion on episulfide’s sulfur to form a thiocarbonyl intermediate. The ylide further attacked this thiocarbonyl intermediate to give the final olefins.
Wittig reaction
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