Cyclopropane ring fragmentation-type

Two unique type Had syntheses of pyrroles that were reported both involved cyclopropane fragmentations. The first allowed for a synthesis of 2-arylpyrroles <06SL2339>. In the event, treatment of stannylcyclopropane 25 with -BuLi followed by benzonitrile produced 2-phenylpyrrole 26 via tin-lithium exchange, addition to the nitrile, ring fragmentation of ketimine intermediate, intramolecular condensation, and loss of dibenzylamine. 

The increasingly common theme of developing new pyrrole syntheses that involve cyclopropane fragmentations appeared in a type Ilae pyrrole synthesis <06OL835>. Treatment of doubly activated cyclopropane 43 with benzylamine in the presence of magnesium sulfate led to complex pyrrole 44 via a nucleophilic cleavage of the cyclopropane ring, intramolecular condensation, and isomerization of the exocyclic JC-bond. 

In contrast, a considerable body of evidence supports the existence of highly polarized intermediates in ring fragmentations of cyclopropane derivatives of type IX. ... 

The presence of a 9,19-cyclopropane ring or a 4-methylene group gives rise to other fragmentation types, fragmentation (a) being greatly... 

A betaine intermediate is formed, the fragmentation of which leads to formation of an oxirane ring by intramolecular substitution by the anionic oxygen (Eq. 89). The sulfonium ylides also react with other types of compounds containing an electrophilic unsaturated bond (C=C, C=N), giving cyclopropane derivatives and aziridines. 

The reaction of cis- and fra j-methyl-substituted l-(trimethylsiloxy)bicyclo[n.l.O]alkanes (n = 3,4,5) is stereospecific. When treated with lead(IV) acetate, followed by diazomethane, these substrates give the methyl ( )- and (Z)-alkenoates, respectively. The reaction is interpreted by assuming electrophilic attack of lead(IV) acetate on the cyclopropane carbon to cleave the ring, followed by a Grob-type fragmentation with lead(II) acetate as the leaving group. 

In contrast to the above findings, irradiation of 2-phenyl-1-azaspiro[2.2]pent-l-ene (243) in methanol resulted in a Griffin-type fragmentation and produced ethylene and 2-phenylazirinylidene (244). Three-membered rings are known to undergo [3- 2- -l] cycloelimination on irradiation.For example, cyclopropane has been photolyzed in the vapor phase and gives methylene and ethylene,while photolysis of ben-... 

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