Cyclopropaniminium ions

The preparation of aminocyclopropane derivatives from substituted chloroenamines showed some restrictions. The substituent influences both the energy difference between aminoallyl cation and cyclopropaniminium ion and a subsequent homoenamine ringopening. Thus, the stabilization of the positive charge in a dibenzotropylium species (237) may be the reason for the formation of 239 from 236 and nucleophiles like OH , HNMe2/AgN03 or RS" So far, only treatment of 236 with sodium borohydride led to aminocyclopropane compound 240 (Nu = H) (equation 56). 

Ring-opening reactions of the distal bond of aminocyclopropanes are of minor importance. Sometimes this type of reaction is observed in nucleophilic substitution of aminobicyclo[3.1.0]hexane derivatives (500) leading to 504 instead of (equation 128). The ring-opening tendency is a consequence of the lower stability of 501 with respect to other cyclopropaniminium ions. ... 

I. Generation, Stability, and Characterization of Free Cyclopropaniminium Ions... 

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. ... 

Earlier reported free cyclopropaniminium ions were characterized by IR (vc=n+ cm" ) and HNMR spectroscopy. Later, CNMR gave more convincing evidence for the presence of a bicyclo[4.1.0]hept-7-ylidenemorpholinium ion (2 signals for the cyclopropane system a singlet at (5 = 204 and a doublet at = 21). ... 

S.2.3.3.2. Generation of Cyclopropaniminium Ions in Nucleophilic Substitution of Cyclopropylamine Derivatives... 

S.2.3.3.4. Nucleophilic Substitution via Cyclopropaniminium Ions from Cyclopropylamine... 

Electron-rich aromatic and heteroaromatic compounds are aminocyclopropylated by a cyclo-propaniminium ion which is generated from a cyclopropanone hemiaminal and titanium(IV) chloride or an acidic reagent. Indole, 1-methylpyrrole or phenol react in this way to give products 3, 4, and 5, respectively. Only C-alkylation at the phenol was observed when dimethylaminocyclopropanol and phenol were stirred in dichloromethane at 20 °C for 48 hours. This contrasts strongly with the alkylation of phenolate by a cyclopropaniminium ion leading to the 0-alkylated product. ... 

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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