Showing papers on "Intramolecular reaction published in 1981"

Diels-Alder reactions of 1-azadienes

Abstract: Preparation de N-acyl aza-1dienes (par ensemble allylidene amide de l'acide pentene-4oique) par elimination thermique de derives O-acetyles d'hydroxylamines. Les azadienes subissent une cycloaddition intramoleculaire pour donner des derives piperidiniques. La reaction a une stereochimie exo predominante

Inter-versus Intramolecular Oligomerization of Nitrile Groups in Polyacrylonitrile

Abstract: Experimental evidence is presented indicating that intermolecular oligomerization of CN groups (leading to crosslinked structures) takes place, and possibly has an even greater importance than the intramolecular reaction (leading to “ladder polymer”), at higher temperatures. The easy, quasi “built-in” crosslinking upon heat treatment is considered the most significant single feature with regard to making polyacrylonitrile and its copolymers unique among synthetic polymers as a carbon fiber precursor.

Carbonyl‐Ylide als Cycloadditionspartner: Intramolekularer Transfer einer ADM‐Einheit

Abstract: Carbonyl Ylides as Cycloaddition Components: Intramolecular Transfer of a DMAD Unit On heating the specifically designed ene-oxirane 6 is cleanly transformed into the 2,5-dihydrofuran derivative 7 As mechanism of this conversion ring opening to carbonyl ylide 8 is proposed followed by formation of the intramolecular cycloadduct 9 which suffers rapid cycloreversion leading to 7. The latter process is precluded in the case of the dihydro derivative 10 which, in fact, reacts under comparable conditions and with equally good yield to give 11 as a thermally stable and sterically pure compound. In the presence of dimethyl acetylene dicarboxylate (DMAD) as external dipolarophile bimolecular cycloadditions do not compete with the intramolecular reaction mode.