Ammonium cyclobutanone

Keteniminium salts undergo [2-1-2] cycloaddition reactions with unreactive olefins, such as ethylene, cyclopentene, cyclohexene and styrol to give cyclobutane ammonium salts 23, which are readily hydrolyzed to give cyclobutanones 24. Likewise, reaction with acetylene derivatives affords cyclobutenylidene ammonium salts 25, which are also readily hydrolyzed to give the cyclobutenones 26. Some of the [2-1-2] cycloadducts obtained from keteniminium salts and olefines are shown in Table 4.17. The keteniminium salts are easily synthesized from suitable dimethylamides and phosgene, or trifluoromethanesulfonic acid anhydride. The reaction of the amide with phosgene generates a chloro compound 21, which is in equilibrium with the ketenimine salt 22. 

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