Abstract
N ,N -Dimethylhydrazones
of propenal- and 2-methylpropenal and their derivatives
and homologues (vinylogous aza-enamines) were allowed to react with N ,N -dimethylformiminium chloride
in moisture-free dimethylformamide to yield singly, doubly, and
even triply aminomethylated products. They can be easily separated
and characterized as crystalline hydrochlorides. The reaction takes
place at the ω-position of the π-system. This
is a consequence of the conjugative interaction of the electron-donating aminohydrazone
group with the double bond system in analogy to the enamines. The
formation of dialkylhydrazones from unsaturated aldehydes thus causes
the umpolung of the formerly electrophilic d³ -building
blocks into a nucleophile. Depending on the reaction conditions
and confirmed by crystal structures and 2D NMR experiments, control
can be exerted over the degree of substitution: Up to trisubstituted
products were obtained for the 2-methylpropenal derivative. The
hydrochlorides can be easily deprotonated to yield the free aminohydrazone
bases. The back-conversion of the aminohydrazones into the corresponding
amino aldehydes is possible under acidic conditions.
Key words
hydrazones - electrophilic substitution - nucleophilic addition - amino aldehydes - umpolung
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25 Crystallographic data (excluding structure
factors) for the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supplementary publication
numbers CCDC-725902 [(Z )-6 ˙HCl], CCDC-725903 [(Z )-10 ˙4HCl],
CCDC-725904 [(E )-12 ˙2HCl], CCDC-725901 [(Z )-21 ˙HCl] and
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be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [Fax: +44(1223)336033; e-mail: deposit@ccdc.cam.ac.uk].
