Pyrrolines from aziridines

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. 

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... 

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. ... 

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. 

Hetm ocycles.—StabiliTed phosphoranes react as nucleophiles with azamethine ylides generated from suitably substituted aziridines or oxazolines. The resulting zwitterionic intermediates undergo intramolecular Wittig reactions to form 3-pyrrolines (Scheme 13). 

Tetrahydropyrrolizines (210) and (211) can be formed via radical scission of either bond a or b in the intermediate vinyl-aziridine (208) but yields are moderate at best and the major product is the monocyclic pyrroline (209), formed by a 1,5-homo-dienyl rearrangement. The route therefore could provide a useful access to the pyrrolizidine framework if conditions could be identified which would allow more controlled and efficient breakdown of (208). The synthesis of substitute pyrrolines by ring expansion of vinyl aziridine derivatives has also been accomplished in a palladium-catalysed reaction. N -Tosyl-2-vinyl five- and six-membered nitrogen heterocycles (213) ace obtained in generally high yields under mild conditions from precursor dienyl nitrogen heterocycles (212) in the presence of a catalytic amount of [Pd(PPh ) ]. The complete diene unit is required for the... 

A range of 3-pyrrolines could be synthesized from conjugated dienes with common nitrene precursors catalyzed by [Cufhfacaclj] via intermolecular [4h-1] cycloaddition. Good to excellent cisltmns selectivity could be obtained when 1,4-disubstituted dienes are used as substrates. The cis or trans preference depends on the nature of the substituents of the substrates. Mechanistic studies disclose that this transformation proceeds through diene aziridination and subsequent ring expansion. The [Cufhfacaclj] catalyst shows higher activity than other copper catalysts [41] (Scheme 8.17). 

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