Enammonium salt with

While an experiment with the proton addition to the enamine was being carried out, a very significant observation was made (5) when an enammonium salt was isolated. A white precipitate was produced when the enamine, synthesized from a-phenylpropionaldehyde and... 

When acidic hydrolysis is carried out with the material supposed to be enammonium salt, (+)a-phenylpropionaldehyde is produced in excess. When the same substance is heated at 60°C for several hours, a levorotatory material is produced in excess. 

The chirality is decided when a porton is added to the enamine nitrogen on the amine group. Furthermore, when rearrangement to the iminium salt occurs, the chirality of the iminium proton is decided by this first proton. Upon hydrolysis of the enammonium salt, water is added from the opposite side of the enammonium proton and asymmetry of the recovered carbonyl compounds results. When an iminium salt with established chirality is hydrolyzed, the resultant carbonyl compound will have the reversed chirality because the hydrolysis occurs at the carbon-nitrogen double bond. 

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. 

A promising alternative to generate cyclopropyl iminium ions, the presumable first intermediates in the Cloke rearrangement, is outlined in equation 32. The enammonium salts have been obtained at room temperature after treatment with lithium bromide in acetonitrile. These very mild conditions should be compatible with many sensitive functional groups. 

Important for the hydrolysis is the observation (10) that protonation of enamines with hydrogen chloride does not immediately lead to immonium salts, but in most, if not all, cases first to the formation of the corresponding enammonium ions, which afterward rearrange more or less rapidly to the more stable immonium ions [Eq. (1)] ... 

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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