Imines sydnone

The term mesoionic was suggested originally to describe compounds of the sydnone (129) or sydnone imine (130) type (49JCS307, 50JCS1542). Since then this term has been applied somewhat indiscriminately to a variety of heterocyclic molecules which can be represented formally as zwitterions. The original, rather restrictive definition put forward by Baker and Ollis (55CI(L)910) was later made even more so by Ollis and Ramsden (76AHC(19)1), and it is this most recent definition which now appears to be the most useful. 

The related sydnone imine hydrochloride 147 has also been isolated in low yield by treating N-nitroso-A -diphenylphosphinylmethylglycinonitrile 146 with anhydrous HQ and ether at low temperature (2), in a manner similar to that described previously for other nitrosamines of aminoacetonitrile (80). 

The chemistry of sydnone imines (2) has been reviewed, and a discussion of their chemistry is not duplicated here. Recent photochemical and pharmacological studies are included in Sections IX and XII. 

Meso-ionic 3-acyl-1-phenyl-1,2,3-triazol-4-ones (190, R = Ph or Me, = H) have been postulated as intermediates in the interesting base-catalyzed transformation of IV-acylsydnone imines (191, R = Ph or Me, R = H) into 4-hydroxy-1-phenyl-1,2,3-triazole (192, R = A similar photochemical transformation (191 190, R = Me or Ph, R = Ph) has also been reported. " A different base-catalyzed transformation of sydnone imine derivatives into pyrazolones has been recently reported. ... 

The investigation of the photochemistry of meso-ionic heterocycles is still rather limited. However, some common mechanistic features can be appreciated in the pathways that have been put forward to account for the products of a number of photoreactions. A summary of the results obtained for various classes of meso-ionic heterocycles follows. Although the decision has been taken not to discuss in detail in this review the general chemistry of sydnones (1) and sydnone imines (2), it is nevertheless appropriate to include in this section the results obtained in the study of their photochemistry. 

For reasons given in the Introduction, the chemistry of sydnones and sydnone imines is not discussed in the chemistry section of the review. Examination of their pharmacological activity is, however, given in this section. 

Further studies on the preparation and activity of sydnofen (451) and sydnocarb (452) have been reported. A number of sydnone imine derivatives have also been described as useful hypotensive agents, vasodilators, muscle relaxants, and monoamine oxidase inhibitors. ... 

A much older reaction of N-nitroso a-aminoacids is their cycli-zation to the mesoionic sydnones (39 0a l 2) more recently, N-nitroso a-aminonitriles have been cyclized to the corresponding sydnone imines (U0, l, 2,43) ... 

N-Nitroso-sydnon-imine lassen sich durch Nitrosierung der entsprechenden Sydnon-imin-Hydrochloride erhalten, dabei konnen beide Reaktionsschritte, Bildung des Sydnon-imin-Hydrochlorids und Nitrosierung, als Eintopfreaktion durchgefuhrt werden. Beim Erwarmen werden diese unter Stickstoff-Eliminierung in die Sydnone ubergefuhrt. 

Ethyl-3-(2-methyl-propyl)-sydnon Eine Losung von 1,98 g (10 mmol) 4-Ethyl-3-(2-mcthyl-propyl)-N-nitroso-sydnon-imin in 7 ml Dimethylformamid wird auf dem kochenden Wasserbad bis zur vollstandigen Entfarbung ( 10 min) erwarmt. Das Losungsmittel wird i. Vak. entfernt und das Rohprodukt aus Diethylether umkristallisicrt Ausbeute 1,67 g (98%) Schmp. 45 46". 

Die Bedeutung der Sydnon-imine liegt in ihrem pharmakologischen Wirkungsspek-trum57-60 61. 3-Morpholino-sydnon-(ethoxycarbonyl-imin) (Molsidomin, INN) ist als Koronar-therapeutikum zugelassen. 

Rl R2. .. -sydnon-imin-Hydrochlorid [%] Schmp. [°C] Lite- ratur... 

Wie die Sydnone lassen sich auch die Sydnon-imine in 1,3-dipolaren Cycloadditionen zu 4,5-Dihydro-pyrazolen und Pyrazolen umsetzen. So erhiilt man aus 3-Phenyl-sydnon-aeyl-iminen durch Reaktion mit Butindisaure-dimethylester 3,4-Dimethoxvcarbonyl-l-phenvl-pyr-azol (30 67%)84 ... 

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