Azomethine ylides, nitrogen-containing

Dipolar addition of azomethine ylides to electron-deficient olefins is a versatile route to nitrogen-containing heterocycles. Applying this approach to ( )-ethyl 3-fluoroacrylates utilizing L-menthol as a chiral auxiliary provides a stereoselective and regioselective synthesis of enantiopure-fluorinated prolines 28 and 29. Careful... 

Five-membered Nitrogen-containing Rings. The addition to alkynes of the azomethine ylide (80), which results from the thermal opening of 2,2-di-methoxycarbonyl-l,3-diphenylaziridine, occurs in both possible orientations giving two isomeric 3-pyrrolines (81). The structure of the products was established by spectroscopic means, and by reduction to known pyrrolidines. 

Allene insertion/nucleophile incorporation can also be combined with 1,3-dipole cycloaddition as an efficient protocol for the synthesis of various fused polycycles. In 2005, Dondas et al. used this strategy to synthesize various nitrogen- or oxygen-containing fused polycycles such as 323 through intermediate azomethine ylides, azomethine imines, and nitrones [112] (Scheme 6.85). 

Interesting structures can be formed by combinations of ring and side-chain substituents in special relative orientations. As indicated above, structures (28) contain the elements of azomethine or carbonyl ylides, which are 1,3-dipoles. Charge-separated species formed by attachment of an anionic group to an azonia-nitrogen also are 1,3-dipoles pyridine 1-oxide (32) is perhaps the simplest example of these the ylide (33) is another. More complex combinations lead to 1,4-dipoles , for instance the pyrimidine derivative (34), and the cross-conjugated ylide (35). Compounds of this type have been reviewed by Ramsden (80AHCl26)l). 

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