Azomethines, addition onto

The tandem reaction of carbenoids with simple imines to form azomethine ylides which then undergo 1,3-dipolar cycloaddition with various dipolarophiles was first reported in 1972.81 Treatment of phenyldiazomethane with copper bronze in the presence of excess N-benzylidenemethylamine resulted in the isolation of imidazoline 170. Formation of this product was rationalized by carbenoid addition onto the imine nitrogen to give azomethine ylide 169 which then underwent a 1,3-dipolar cycloaddition with another molecule of imine to produce the observed product. Bartnik and Mloston subsequently extended this observation by using other dipolarophiles.82 For example, catalytic decomposition of phenyldiazomethane and A-benzylidenemethylamine in the presence of dimethyl maleate or benzaldehyde gave pyrrolidine 171... 

By using the same type of 1,3-dipolar cyclo-addition of azomethine ylides it was possible to anchor ferrocene (Fc) onto the sidewalls of SWCNTs [96]. Accordingly, a nitrogen-functionalized glycine (R-NHCH2COOH, R= CH2CH2OCH2CH2OCH2CH2NHCO-FC) and paraformaldehyde were refluxed in dimethylformamide in the presence of SWCNTs. From differential scanning calorimetry the extent of functionalization was determined as approximately 1 Fc molecule per 100 carbon atoms of the SWNTs. 

On the other hand, the use of the suitable combination of a metal salt, chiral ligand, and base promotes at low temperature the formation in situ of chiral A-metalated azomethine ylides from the corresponding iminoester and the subsequent selective cycloaddition onto the fullerene cage. Thus, the P,S chiral ligand Fesulphos along with copper(II) acetate directs the addition toward the formation of the stereoisomer (25, 55)-2-alkoxycarbonyl-5-arylpyrrolidino[3,4 l,2][60]fullerene with complete cis diasteroselectivity and enantiomeric excesses up to 93% (Scheme 34.9). 

The addition of polar organometallics onto carbon-nitrogen double bonds opens a versatile entry to amines. Lithium acetylides often require activation by boron trifluoride to display full reactivity. Azomethines derived from crotyl or cinnamyl... 

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