Cyclopropaniminium salts

Substituted bicyclo[ . 1.0]alkanes may also be obtained by condensation of secondary amines with 2-haloketones. A variety of nucleophilic reactions can be carried out on the intermediate cyclopropaniminium salt 116251 (Scheme 108). Competing alkene scission and cyclopropanation occurs on reaction of enamines with pentacarbonyl-chromium carbene complexes252 (Scheme 109). N-Silylated allylamines and their derived N-silylated enamines undergo rhodium or copper catalysed cyclopropanation by methyl diazoacetate253 (Scheme 110). 

Cyclopropaniminium salts have been prepared in solution from cyclopropane-1,1-diamines by addition of methyl fluorosulfate, - bromine in liquid sulfur dioxide or dimethylchloronium tetrafluoroantimonate in liquid sulfur dioxide. Bicyclo[4.1.0]heptaniminium salts were obtained in fluorosulfonic acid at — 60 °C from a bicyclo[4.1.0]heptanone aminal or hemiaminal precursor or by the reaction of the corresponding aminal and methyl fluorosulfate in chloroform. A free cyclopropaniminium ion in solution also was assumed to be generated by the interaction of cyclopropanone hemiaminal with titanium(IV) chloride at — 78°C in di-chloromethane. ... 

On heating above 50 °C, the methyleneaziridinium salts 2 rearrange to cyclopropaniminium ions 3. Dialkylaziridinium ions such as the A,(V-dimethylaziridinium species, thereby, produce stable cyclopropaniminium ions (stable up to 150 °C in fluorosulfonic acid, see Section 5.2.3.3.1). In the case of protonated methyleneaziridinium ions 2 (R = H, Y = FSO3 ) the cyclopropaniminium salts 3 from the rearrangement are less stable leading to vinylammonium salts as the final product. 

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