Synthese et reactivite comparee d'alkoxy et de thioalkoxymethylenecetenes

Application of Flow Thermolysis in Organic Synthesis: Easy Access to α,ω-Bis Thienyl- and Bis Pyrrolyl- Alkanes from Methylene Derivatives of Meldrum's Acid

“…Thus, whereas the ω−aminoalkyl or hydroxyalkyl aminomethyleneketenes (X= NR'; Y=NMe,O ; n=2-12) essentially led to enaminolactams or lactones 5 [7,8] the alkylsulfanyl methyleneketenes 2 bearing a large functionalised hydrocarbon chain (X=S; n >3) only provided hydroxythiophenes 9. The absence of large sized lactones or thiolactones 5a,b well illustrates the specific thermal behaviour of these alkylsulfanyl methyleneketenes 2a,b: the 1,4-hydrogen migration involving the rearrangement of 2a,b into planar dipolar species 7a,b [3,10] seems to be favored in that case; on the contrary, the intramolecular addition was favored in the case of alkylsulfanyl intermediates 2 with smaller ω−mercapto or ω-hydroxyalkyl chains (n=1-2) [9] .…”

“…The highly reactive hetero-substituted methyleneketene intermediates 2 can be easily generated by thermolysis of the corresponding Meldrum's acid derivatives 1 [1][2][3][4] and can undergo various thermal reactions depending on the nature of both the heteroatom X and the chain (CH 2 ) n Y. Alkoxymethyleneketenes 2 (X=O; Y=H; R=H,CH 3 ) are reasonably stable in solution at room temperature, and seem to be the most stable ones [3] . …”

Formation of isomeric pyrrolones by flash vacuum pyrolysis of bisaminomethylene derivatives of Meldrum’s acid

“…9 In addition, a concerted hydrogentransfer-cyclisation process from the methyleneketene 3 can be excluded because the configuration of an asymmetric center at the site of hydrogen transfer (e.g., Scheme 1, R 1 = Pr i , R 2 = Me, R 3 = Ph) is partially lost in the final pyrrolone. 10 It has been proposed that it is the 1,5-dipolar species 4 which undergoes the final electrocyclic ring closure to give the products 5 in both the nitrogen and the sulfur series, [9][10][11] but why are such intermediates not observable spectroscopically?…”

Flash‐Vakuumpyrolyse – Techniken und Reaktionen

“…[166] Seitdem durchgeführte Experimente mit einem Pulsstrahl-Fourier-Transform-Spektrometer haben eine deutlich verbesserte Auflçsung des Didehydrobenzol-Mikrowellenspektrums ergeben. (44)] und durch Matrix-IR-Spektroskopie,M assenspektrometrie,P hotoelektronen-und Millimeterwellenspektroskopie wie auch Tieftemperatur-13 C-NMR-Spektroskopie umfassend charakterisiert. [168] Diese Isocyanogen, CN-CN,w urde durch FVP von Norbornenonazin (91)w ie auch von 2,3-Diphenyl-N-cyaniminocyclopropen (92)g eneriert [Gl.…”

“…[43] Allgemein sind Methylenketene mit n-Donor-Substituenten (NR 2 oder OR) relativ stabil und fürSynthesezwecke durch präparative FVP leicht herstellbar. [44] Darüber hinaus cyclisierte 8 bei 800 8 8C über das N-Methylid 9,d as durch 1,4-H-Verschiebung gebildet wurde,z u 10. [45,46] Eine weitere N-Ylid-Cyclisierung über eine einbezogene 1,6-H-Verschiebung führt zu Azepin-3(2H)-onen 11 in 64-75 %A usbeute (Schema 3).…”