Aziridines pyrrolines

Azomethine ylides (Section 4.03.6.1.1) have been generated from a wide variety of aziridines using both thermal and photochemical methods. With carbon-carbon unsaturated dipolarophiles, pyrrolines or pyrrolidines are obtained. With hetero double bonds, however, ring systems of interest to this discussion result. 

Thermal rearrangement of 2-vinylaziridine 203, with an electron-withdrawing substituent on the nitrogen atom, at reflux in decalin predominantly yielded 2-pyr-roline 204 along with some 3-pyrroline derivatives 205 (Scheme 2.50) [79]. A similar reaction was also observed with l-alkyl-2-phenyl-3-vinylaziridines 206 [80]. From these observations, the nature of the products formed depends on the natures of the substituents on the aziridine ring if the ring carbon carries a phenyl substituent, the thermolysis in most cases preferentially yields 2-pyrrolines. 

Microwave irradiation in solvent-free conditions induces the cleavage of the 2,3-bond of 2-aroyl-aziridines 135 to give an azomethine ylide intermediate, which subsequently undergoes cycloadditions to a multiple bond and leads to oxazolidine, imidazoline, naphthooxazole and pyrroline derivatives 136 in good yields (Scheme 9.41) [32b], Reactions were performed at atmospheric pressure in an Erlenmeyer flask placed in a commercial domestic oven. The reactions were complete in 10-15 min while the conventional method requires 18-20 h. 

Cleavage of aziridines has been employed in the asymmetric total synthesis of pancratistatin 57 [47], a compound that is the object of considerable attention thanks to its broad spectrum of antineoplastic activities [48]. The chemistry of vinylaziridines has for the most part been confined to their use in rearrangement sequences resulting in functionalized pyrrolines. Hence, because of the lack of data concerning the ring-opening of vinylaziridines with carbon nucleophiles,... 

DMAD led to compounds 46 and 47 in good yield. The pyrroline (47) was resistant to oxidation, and selenium dioxide in a sealed tube at 200° had to be used the stability of 47 is a major reason for the structural assignment with the hydrogens in a trans relationship since the authors reason that a cis geometry would favor oxidation. The experimental data suggested that 46 did not come from 47 but was derived from the initially formed 3-pyrroline (44). These aziridines have also been... 

Vinyltriazolines are unique thermolysis leads to high yields of 1-vinylaziridines. This is true of fused-ring tetracyclic (Scheme 40)199,201 and tricyclic triazolines (Schemes 42 and 43)200 204 with vinylic substitution in the 1-position. 1-Vinyltriazoline with no substituents on the ring carbons furnishes 1-vinylaziridine without formation of pyrrolines.378 Thermal decomposition of vinyl azides in acrylic acid derivatives is a synthetic route for 2-substituted 1-vinylaziridines.470 Similarly, aziridine 1-oximes are the only products of thermolysis of triazoline 1-oximes.107... 

Alkenyl aziridines are useful synthetic building blocks and can be converted to allylamines by conjugate addition of organocuprates [29], to pyrroline derivatives by rearrangement [30] and to P-lactams by Pd-catalyzed carbonylation [31]. 

The adduct 65 of aziridine to the acetylenic phosphonium salt 64 readily rearranges to the enamine 66, which in refluxing acetonitrile is converted into the pyrroline derivative 68 by opening of the aziridine ring and recyclization of the resulting zwitterion 67 (equation 33)54. 

When reacted with 1-aryl-3,3,3-trifluoropropynes, azomethine ylide 14, generated from the aziridine, provides pyrrolines in high yield, with no rcgioseleclivily. These cycloadducts can be converted into the corresponding pyrroles or pyrrolidines. ... 

The intermediate bicyclic vinyl dihydro triazoles were generally not isolated, as they are unstable. By thermal decomposition, the vinylaziridines were converted to regioisomeric bicyclic pyrrolines 1 and/or 2, with different substitution patterns, depending on the nature of the substituents. Under the same conditions a 1,5-homodienyl shift can take place to give a monocyclic pyrroline 3. Nucleophilic displacement by iodide ion, however, regioselectively cleaves the C-N bond of the aziridine ring, giving 2 exclusively. 

As early as 1965, the first example of the the carbon-carbon bond cleavage of an aziridine generating an azomethine ylide 1,3-dipole was reported by Heine and Peavy (65TL3123). This also offers the first generation of acyclic azomethine ylides by the aziridine route. Thus, 1,2,3-triphenylaziridine, with its stereochemistry unspecified, was heated under reflux in toluene in the presence of diethyl acetylenedicarboxylate. The azomethine ylide (1) generated was captured by the acetylene to give a quantitative yield of diethyl l,2,5-triphenyl-3-pyrroline-3,4-dicarboxylate. 

Osowska-Pacewicka, K., Zwierzak, A. Reactions of N-phosphorylated aziridines with dianions derived from ethyl acetoacetate and 1,3-diketones new route to substituted pyrrolines and pyrrolidines. Synth. Commun. 1998, 28,1127-1137. 

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