Iminium salts, addition hydrolysis

The reaction of iminium salts such as 66 with salts of trichloroacetic acid has been shown to yield amides such as 84 on hydrolysis 126). It was suggested that the reaction proceeds by addition of dichlorocarbene to give an aziridinium intermediate (85), which was opened by trichloroacetate followed by hydrolysis to give the observed products 126). The observed products from the reaction can be accounted for by formation of CCI3,... 

Epoxynitrone (742) can be transformed to a positively charged heterodiene (743) using CF3S03SiMe3 or CF3S03Si(Bu )Me2 as electrophilic reagents (79HCA205). The diene adds to isolated double bonds to afford oxazines such as (744) via an inverse electron demand Diels-Alder pathway. Subsequent addition of cyanide to the iminium salt leads to a stable derivative (745) which can be converted through its mesylate (746) to an a-methylene y-lactone (747) on base treatment followed by acid hydrolysis (Scheme 171). 

When cesium fluoride is used instead of zinc chloride, a diaminomethane derivative is obtained, whose formation is explained by the addition of the iminium salt to the secondary amine resulting from its hydrolysis.219... 

Further reduction and subsequent elimination of the alkoxyaluminate leads to an intermediate iminium salt (31). Addition of another hydride (as in 32) and hydrolysis gives the amine.3 As the steric hindrance on... 

Iminium halides are intermediates in the hydrolysis of nitriles and in a variety of chemical reactions. For example, in the Ritter reaction addition of a nitrile or hydrogen cyanide to a carbonium ion occurs, leading to the intermediate formation of a nitrilium salt. Nitrilium salt intermediates have also been postulated in the Schmidt reaction and in the Beckmann rearrangement, provided the latter was performed in concentrated sulfuric acid. However, since we are predominantly concerned with imidoyl halides, these reactions are not discussed in this monograph. 

Michael additions [63] and is now established as a general strategy for the asymmetric conjugate addition of nucleophiles at the (3-position of a,(3-unsaturated carbonyl compounds. The standard catalytic cycle for a chiral pyrrolidine-catalyzed (3-functionalization of an a,(3-unsaturated carbonyl compound is shown in Scheme 2.12, and it begins with the acid-promoted condensation of the carbonyl with the amine to form an unsaturated iminium ion, more electrophilic than the starting unsaturated carbonyl. This reactive intermediate suffers then the addition of the nucleophile at the (3-position, leading to a (3-functionalized enamine in tautomeric equilibrium with an iminium ion. Hydrolysis of this intermediate releases both the product and the chiral ammonium salt, which can reenter the catalytic cycle. 

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