Keteniminium chloride

Diels-Alder reactions. The amino group at Ci renders this position electrophilic, whereas C4 is nucleophilic (push-pull diene). The diene (1) can react as a vinyl keteniminium chloride (la) in reactions with simple nitriles such as acetonitrile or acrylonitrile. After treatment with base a pyridine derivative (2) is obtained. The... 

The final position for potential asymmetric induction is that which ultimately becomes the C-2-carbonyl group of the p-lactam. Ghosez [57] reported a unique method involving cycloaddition of keteniminium chlorides with imines. Reaction of amide 87 with phosgene gave 88 which when treated with base generated the keteniminium chloride which underwent cycloaddition with high asymmetric induction. Conversion of the adduct to the desired product required conversion to the azetidinone-thione and oxidative conversion to the trans- -lactam 89 (Scheme 11). 

P-Disubstituted a-chloroenamines are readily converted into the corresponding keteniminium salts (33) in the presence of a Lewis acid (equation 68). Silver tetrafluoroborate, zinc, tin and aluminum chlorides have been successfully used. 3-Disubstituted keteniminium salts have been isolated and characterized. " Unlike the corresponding ketenes, they do not dimerize or polymerize. However, they readily undergo [2 + 2] cycloaddition reactions with unsaturated substrates. ... 

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