Allyl enammonium salts

Fig. 19 Allyl enammonium salts are encapsulated within the supramolecular assembly, promoting electrocyclization to the corresponding iminium cation. This cation is subject to hydrolysis in basic solution, yielding the aldehyde products while promoting catalytic turnover... 

McComsey, D. F., Maryanoff, B. E. 3-Aza-Cope Rearrangement of Quaternary N-Allyl Enammonium Salts. Stereospecific 1,3 Allyl Migration from Nitrogen to Carbon on a Tricyclic Template. J. Org. Chem. 2000, 65,4938-4943. 

That the rearrangement occurs with the enammonium salt has been confirmed by the fact that N-allyl-A methylisobutenylamine (154), which is stable under the reaction conditions, affords aldehyde 155 by treatment with methyl tosylate followed by hydrolysis (equation 33)103. MeOTs acts as a promoting reagent which facilitates the rearrangement. Other electrophilic reagents110-112 have also been employed to create a quaternary nitrogen center in order to accelerate the 3-aza-Cope rearrangement. 

The acceleration of the 3-aza-Cope rearrangement of A-allylenamines through formation of a cationic quaternary nitrogen center (enammonium salt) has obvious advantages. However, direct allylation of enamines in order to form the enammonium ions is unsatisfactory, and difficult. Moreover, the rearrangement-hydrolysis product is often contaminated by the C-allylated product when an unsymmetrical allyl halide is employed... 

In the last few years, several groups have developed enantioselective domino reactions catalysed by combinations of organocatalysts with palladium complexes. As an example, Murkheqee and List have reported a domino synthesis of p-all earbon quaternary amines on the basis of a highly enantioseleetive a-allqrlation of a-branched aldehydes, involving an achiral palladium catalyst and a chiral phosphoric acid. Under the catalysis of phosphoric acid, a secondary allylamine reacted with an a-branehed aldehyde to form an enammonium phosphate salt, which upon reaction with palladium catalyst afforded a cationic 7t-allyl palladium complex (Scheme 7.2). This intermediate resulted in the formation of an a-allylated iminium ion, whieh eould be reduced to the corresponding final chiral amine in high yield and exeellent enantioselectivity of 97% ee. The synthetic utility of this transformation was also demonstrated hy a formal synthesis of (+)-cuparene. 

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