Reaktion von Triphenylphosphin-alkylenen mit aktivierten Doppelbindungen

Abstract

Die in der Tabelle angefuhrten Ausbeuten wurden bei Testreaktionen rnit kleinen Ansatzen erreicht. Sie erheben keinen Anspruch auf Maximalausbeuten und sind stark abhlngig von der Konzentration der Diazoverbindung. Bei der Reaktion rnit Benzalchlorid oder Benzalbromid wurden samtliche Komponenten in Hexan wahrend 12 h auf 70°C erwiirmt. Beiprodukte sind Azin (ungef. 20% d.Th.) und polymeres Material. Eingegangen am 10. Januar 1962 [Z 2071._

Stereoselective Synthesis of Polysubstituted Alkenes through a Phosphine‐Mediated Three‐Component System of Aldehydes, α‐Halo Carbonyl Compounds, and Terminal Alkenes

“…The resulting phosphorus ylide D could react with aldehyde 1 to give alkene 3. Alternatively, phosphorus ylide D (R 3 = H) might undergo Michael addition to the electrondeficient alkene [8] and subsequent proton transfer to generate phosphorus ylide F. Thus, a phosphine-mediated onepot, three-component reaction of aldehyde 1, a-halo carbonyl compound 2, and an electron-deficient alkene could be developed to afford trisubstituted alkene 4. The appropriate choice of a phosphine and electron-deficient alkene was anticipated to prevent unwanted side reactions such as the Rauhut-Currier [6a] and Morita-Baylis-Hillman reactions.…”

“…The treatment of w-bromo aldehyde 5 with triphenylphosphine and acrylamide in 1-propanol at 60 8C resulted in the formation of 13-membered a,bunsaturated macrolide 6 in 57 % yield and with exclusive E selectivity [Equation (1)]. [15] Although stable phosphorus ylides were reported to undergo Michael addition to electron-deficient alkenes, [8] in the triphenylphosphine/methyl acrylate-mediated one-pot Wittig reaction of benzaldehyde (1 a) with ethyl a-bromoacetate (2 a) ( Table 2, entry 1) we did not obtain any product resulting from the three-component assembly of benzaldehyde (1 a), ethyl a-bromoacetate (2 a), and methyl acrylate according to our design shown in Scheme 1. Realizing that the Wittig reaction of the in-situ prepared phosphorus ylide proceeded much quicker than its Michael addition to methyl acrylate, we postponed the incorporation of benzaldehyde (1 a) into the multicomponent system.…”

Application of novel sulfonamides in enantioselective organocatalyzed cyclopropanation

“…Here, the nucleophile undergoes an intermolecular Michael addition to a a,b-unsaturated carbonyl compound, and thus forms an enolate; this step is followed by an intramolecular ring closure with loss of a leaving group, present either on the Michael acceptor or on the initial nucleophile, thus furnishing a cyclopropanated product. 5 The most commonly employed nucleophiles in this kind of reaction are a-halocarbanions, 6 sulfur ylides, 7 phosphorous ylides, 8 arsenium ylides, 9 and telleronium ylides. 10 This methodology allows for a wide range of structurally divergent substrates to be reacted and may thus be used to create a plethora of cyclopropane architectures.…”

Site-Selective C–H Alkylation of Diazine N-Oxides Enabled by Phosphonium Ylides

“…Phosphonium ylides are conventionally utilized for olefination reaction with carbonyl compounds . Moreover, phosphonium salts have been employed in Michael additions, organocatalytic Mannich reactions, and other alkylation reactions . Recently, our group first demonstrated the metal-free site-selective C–H alkylation of pyridine and quinoline N -oxides using Wittig reagents. Other alkyl sources were also utilized for the metal-free C–H alkylations of heterocyclic N -oxides. − Due to the widespread relevance of diazine molecules in recent drug discovery, we herein describe the metal-free site-selective alkylation of diazine N -oxides using phosphonium ylides to furnish alkylated diazines.…”

“…7 Phosphonium ylides are conventionally utilized for olefination reaction with carbonyl compounds. 8 Moreover, phosphonium salts have been employed in Michael additions, 9 organocatalytic Mannich reactions, 10 and other alkylation reactions. 11 Recently, our group first demonstrated the metal-free site-selective C−H alkylation of pyridine and quinoline N-oxides using Wittig reagents.…”