Die Reaktion von E‐ß‐Nitro‐styrolen mit Pyrazolidon‐(3)‐azomethiniminen – eine nicht‐cisoide 1,3‐dipolare Cycloaddition

Publisher Website
Google Scholar
Abstract
The Reaction of E‐ß‐Nitro‐styrenes with 3‐Pyrazolidone‐azomethinimines – a Non‐cisoid 1,3‐Dipolar CycloadditionNormal flipping at both ring‐N‐atoms postulated, the thermal addition of E‐β‐nitro‐5a or E‐(4‐chloro‐β‐nitro)‐styrene 5b to 3‐pyrazolidone‐azomethinimine‐1,3‐dipoles 4a or 4b formally can yield 8 isomeric pairs of enantiomers, 4 of which are “permitted”(cisoid) and 4 of which are “forbidden” according to the concerted [π4s + π2s]‐mechanism. If the addition of 5 to 4 is regiospecific, 2 “permitted”(cisoid) (1 and 6) and 2 “forbidden”(3 and 10) isomers are conceivable. From pure 5a and 4a we regiospecifically got 1ref,3trans‐diphenyl‐2cis‐nitro‐6a (75%) and 1ref,3trans‐diphenyl‐2trans‐nitro‐5‐oxo‐perhydropyrazolo[1,2‐a]pyrazol 10a (25%), from 5b and 4b the corresponding bis(4‐chloro‐phenyl)‐isomers 6b and 10b. The sodium salts 8a, b, gained from 6a, b and 10a, b, are identical. With H⊕ (D⊕) in water (D2O) 8a, b give 6a, b (2‐deutero‐6a, b = 7a, b). The 1H‐n.m.r. spectra of 6a, b, 7a, b, 8a, b, 10a, b, and of the 2‐amino‐isomers 11a/12a, corresponding to 6a/10a, are discussed.For the first time products of a non‐cisoid 1,3‐dipolar cycloaddition (10a, b) were isolated. In the discussion (E ⇌ Z)‐isomerization of 5a, and conceivable mechanisms of isomerizations 6a → 10a are excluded. Theoretical consequences are suggested.