Protonated cyclopropane from amines

Though the bulk of the products are not formed from protonated cyclopropane intermediates, there is considerable evidence that at least in 1-propyl systems, a small part of the product can in fact arise from such intermediates.23 Among this evidence is the isolation of 10 to 15% cyclopropanes (mentioned on p. 325). Additional evidence comes from propyl cations generated by diazotization of labeled amines (CH3CH2CD2, CH3CD2CH2, CH3CH2I4CH2 ), where isotopic distribution in the products indicated that a small amount (about 5%) of the product had to be formed from protonated cyclopropane intermediates, e.g.,24... 

It is supposed that the nickel enolate intermediate 157 reacts with electrophiles rather than with protons. The successful use of trimethylsilyl-sub-stituted amines (Scheme 57) permits a new carbon-carbon bond to be formed between 157 and electrophiles such as benzaldehyde and ethyl acrylate. The adduct 158 is obtained stereoselectively only by mixing nickel tetracarbonyl, the gem-dibromocyclopropane 150, dimethyl (trimethylsilyl) amine, and an electrophile [82]. gem-Functionalization on a cyclopropane ring carbon atom is attained in this four-component coupling reaction. Phenyl trimethyl silylsulfide serves as an excellent nucleophile to yield the thiol ester, which is in sharp contrast to the formation of a complicated product mixture starting from thiols instead of the silylsulfide [81]. (Scheme 58)... 

Sol 9. (d) Aldehydes and ketones having a-protons react with secondary amines to form enamines. The enamine formed in the first step undergoes cyclopropanation reaction at the double bond with dichlorocarbene that is generated by a-elimination of HCl from chloroform. This product undergoes ring expansion to furnish 2-chlorocyclohex-2-en-l-one (I). 

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