Immonium cations initiators

The fonnation of an immonium ion from amides and urethanes is under kinetic control at the stage where a proton is lost from the radical-cation initially formed. In the cases of derivatives of uesymmetrical secondary amines, this leads to preferential reaction at an N-CHaR group rather than at N-CHR2 and the kinetically... 

Synthetic work in this area includes a new, stereospecific synthesis of sparteine and a synthesis of isosophoramine. The reduction of quinolizidone (16) by means of lithium aluminium hydride affords, as noted previously, a dimeric product (17), presumably via condensation of the initially formed enamine (18) with the corresponding immonium cation (19). With di-isobutyl aluminium hydride the yield of (17) can be increased to 85%. Analogous reduction of the dilactam (20), prepared by base-catalysed condensation of the bromo-lactam (21) with a-piperidone, gave an intermediate (22), in which the enamine and immonium ion units are present within the same molecule. Intramolecular cyclization of (22), via a transition state derived from the conformation (23), spontaneously gave the... 

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