Electrophilic Addition and Isomerization Reactions of Cyclopropanes

Early work has been reviewedand we will therefore concentrate attention on the most recent work. 

Reaction of cyclopropane with aqueous sulfuric acid results in a small amount of exchange into unreacted cyclopropane and for the reaction is 1.56. These 

TABLE 7. Relative rates of acetolysis of cyclopropanes . Reprinted with permission from J. Am. Chem. Soc., 107, 1003. Copyright (1985) American Chemical Society 

TABLE 8. Relative rates and deuterium isotope effects for acetolysis of some cyclopropanes 

Bromine addition to cyclopropanes is slow in the absence of light unless the ring is heavily substituted . In the presence of light, reaction is rapid since halogen radical attack on substituted cyclopropanes is fast even at — 78°C. In the presence of light, HBr is produced and cyclopropane reacts more competitively with proton acids than with bromine. Addition reactions to cyclopropane are generally slow in the absence of acid catalysts and therefore the conjugate acid is probably involved in reaction. The more facile reaction of cyclopropane with HBr compared with bromine is in contrast with alkene chemistry where bromine addition is the more rapid  

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