N- -imines

The mechanism of attack of 1,3-dipolar reagents on fluoroalkenes can be considered to be either stepwise or concerted. Heteroaromatic N-imines react by a stepwise 1,3 addition to perfluoroalkenes and -alkynes to give fluorinated pyrazolo[l,5-a]pyridines [82JCS(P1)1593]. Pyridinium /-butoxycarbonylmethylide with fluoroalkenes gave pyrrolo[l,2-a]pyri-dines [86JCS(P 1) 1769] and indolizines (22) are obtained with pyridinium phenacylide [91JFC(51)407]. 

In marked contrast to the other hetero atom multiple bond functions cited in this section the >C=N- imine bond was not found to undergo hydrometalation. Imines with neighboring C-H bonds as in PhCH=NMe do react with 1 via imine/enamine tautomerism, but not by hydrozirconation [197]. 

Compounds of types i, 2, and 3 were deduced to have planar, trigonal configurations from kinetic and stereochemical observations71 however, confirmation of this postulate was provided only a few years ago by the X-ray structure analysis of (bistrimethylsilyl)aminobis(trimethylsilylimino)phosphorane8). The P/N(imine) bonds were found to be relatively short, which was attributed to a high rc-bonding component in the planar system of coordinatively unsaturated phosphorus. 

TV-Iniine dimers 7 reacted with 2,3-diphenylazirine to give (76JOC2739) the corresponding pyridotriazines 8. Pyridinium N-imine was useful as a trapping agent for transient azirine. 

Reaction of the C=N imine function - though this is not an isolated imine function but is part... 

Pyridine, on the other hand, is more reactive than benzene towards nucleophilic aromatic substitution. This is effectively reaction towards the C=N imine function, as described above. Attack is... 

Heteroaromatic N-Imines H.-J. Timpe, Adv. Heterocycl. Chem., 1974,17, 213-255. Chemistry of the Heterocyclic N-Oxides , A. R. Katritzky and J. M. Lagowski, Academic Press, New York, 1971. 

A recent example of this is a crystal structural analysis of the zinc complex of the inline derived from 2-pyridinealdehyde and cis,cis,cis-l,3,5-triaminocyclohexane which shows the metal to be in a trigonal prismatic environment (Zn—N (pyridine), 2.211-2.282 A Zn—N (imine), 2.142-2.167 A).320... 

The free carbonyl function of this ligand may undergo further condensation reactions. With amines RNH2, products [PdLL l are obtained where both L and L may be N,N -bonded chelates (42 R = Me, Et, Pr, Bu)264,265 or L may be bonded through N(imine) and 0(oxime) (43 R = H).266 Similar linkage isomerism is seen for other oximato ligands of this type.267... 

The IR spectrum of 8 has been reported (63FRP2166), and the UV spectra of some 1,2,3-benzothiadiazines have been reviewed (70CRV593). Mass spectrometry has been used to establish the structure of 1,2,3-thiadiazines 24, and the fragmentation pattern enabled the alternative isothiazol-N-imines to be ruled out (750MS579). 

Tamura, Y., Ikeda, M., Advances in the Chemistry of Heteroaromatic N-Imines and N-Aminoazonium Salts, 29, 71. 

Condensed 4-nitropyrazoles have been produced from pyridinium N-imines and l,l-bis(methylmercapto)-2-nitroethylene 2-methylthio-l-nitropyrazolo[l,5-a]pyridines (54) (40-60%) are so obtained.49 After the electrocyclic transformation, the intermediate 53 does not lose the elements of nitrous acid, but rather undergoes dehydrogenation to yield the observed products (Scheme 11). Isoquinolinium (V-imine gives 2-methylthio-l-nitro-pyrazolo[5,1 -a]isoquino ine similarly.49... 

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