Kumulierte Ylide, XII. Eine stereoselektive Synthesemethode für (Z)‐α,β‐ungesättigte Aldehyde²⁾

Abstract

2-Ethoxyvinyl)triphenylphosphonium-bromid (5) lafit sich rnit Natriumamid in das korrespondierende Phosphaallenylid 6 uberfiihren, das Ethanol zum Ylid 7 addiert. 7 wird auch aus 5 rnit Natriumethylat erhalten. Die Wittig-Reaktion von 7 rnit Aldehyden 2 verlauft rnit hoher (Z)-Stereoselektivitat. Die entstehenden (Z)-a,O-ungesattigten Acetale 8 lassen sich unter Einhaltung definierter Bedingungen mit p-Toluolsulfonsaure oder durch feuchtes Kieselgel zu den (Z)-a,pungesattigten Aldehyden 9 spalten.(2-Ethoxyvinyl)triphenylphosphonium bromide (5) is converted with sodium amide into the corresponding phosphaallenylide 6 which adds ethanol forming the ylide 7. 7 is also obtained by the reaction of 5 with sodium ethanolate. The Wittig reaction of 7 with aldehydes 2 proceeds with high (Z)-stereoselectivity to give (Z)-a, O-unsaturated acetals 8 which are cleaved under well defined conditions with p-toluenesulfonic acid or with wet silica gel to (Z)-a,p-unsaturated aldehydes 9.

Flash vacuum pyrolysis of argentilactone

“…At temperatures below 650 8C the pyrolysate consisted almost exclusively of unreacted starting material; no ring-opening or thermal isomerisation of the alkene [16] took place under these conditions. At higher temperatures, the major identified nongaseous product was 2-octenal 7, as a mixture of Z-and E-isomers [14,15]. The identity of the product was confirmed by independent synthesis (see Section 2); in particular the configuration of the alkene followed from the magnitude of the coupling constant (E: 3 J 15.6 Hz, Z: 3 J 11.5 Hz).…”

“…A white solid was obtained that melted upon warming to afford a clear liquid pyrolysate (66 mg, 94%), which was found to be a 97:3 mixture of E-and Z-2-octenal 7b and 7a. The isomers were identified by their individual E and Z aldehyde proton doublets at d H 9.46 [14] and d H 10.03 [15], respectively and characteristic coupling constants of 3 J 15.6 and 3 J 11.5, respectively.…”

Reactions of N-PIII-Phosphorylated Trifluoroacetamides with (Ethoxycarbonyl)triphenylmethylide

“…The 31 P NMR spectrum of heterocumulene IV shows signals at 18.2 and 180.4 ppm ( 4 J PP 9.2 Hz). Evidence for the presence in compound IV of sp-and sp 2 -carbon atoms is provided by the 13 C NMR spectra (see Experimental) that are consistent with the spectra of ethoxyphosphaketene acetals [6]. Compound IV is a representative of previously unknown O3P III -phosphorylated phosphaketene acetals [7].…”

Stereoselective Synthesis of (2E,4Z)‐Dienamides Employing (Triphenylphosphoranylidene)ketene

“…70:30 from the corresponding aldehydes 12a-e by Horner-Wadsworth-Emmons olefination employing ethyl (di-o-tolylphosphono)acetate (Scheme 3). Subsequent reduction to the respective allyl alcohol with DIBAL in THF at -78°C, followed by oxidation with MnO 2 in hexane at room temperature gave the target (2Z)-alkenals (Z)-10a, [28] (Z)-10b, [29] and (Z)-10c-e.…”