Recent Developments in the Stereochemistry of Cyclopropane Ring Opening

Abstract

6-Methylspiro[2.5]octan-4-one (62) is obtained by a similar synthesis from (+)-3-methylcyclohexanone ( 6 1 ) [ 3 4 1 . Compound (62) is the first cyclopropyl ketone whose absolute configuration has been determined. Its Cotton effect does not correspond to the predictions of the octant rule.No ring expansion takes place on dehalogenation of 2,2-bis(bromomethyl)cyclohexanone with zinc; the spiro ketone is formed quantitatively in aqueous methanol after a normal ring closure. The higher cycloalkanone derivatives exhibit both reactions. 2,2-Bis(bromomethy1)cyclooctanone (63) is particularly interesting in this respect, since it can be reduced to the ring expansion product (64) in acetic anhydride/ ether, to a mixture of (64) and the normal ring closure product (65) in aqueous methanol, or exclusively to the ketone (65) in aqueous methanol in the presence of ethylenediaminetetraacetic acid. This review article deals with the stereochemistry of the following ring opening reactions: I . Homoallylic rearrangement of secondary and tertiary cyclopropyl alcohols in the presence of electrophilic reagents, 2. The addition of carboxylic acids to vinylcyclopropanes, 3. The thermal rearrangement of vinylcyclopropanes into cyclopentenes. An account is also given of the N M R spectroscopic determination of the conformations of substituted vinylcyclopropanes.

Selective Carbon–Carbon Bond Cleavage of Cyclopropanols

“… The authors describe the mixture of products in this acid-mediated ring opening as being the result of a poorly selective S E 2 reaction, in which the protonation is poorly sensitive to the identity of the substituents on the cyclopropane ring. The acid-mediated ring opening of cyclopropyl alcohol derivatives, and synthetic applications of this transformation, has been previously discussed in detail. ,,− Using either Brønsted or Lewis acids, this reactivity has been featured in numerous contributions to the formation of carbonyl-containing products, substituted allyl products, as well as various-sized cyclic and bicyclic compounds. While not using a stoichiometric acid outright, there is also a report by de Meijere and co-workers featuring the solvolysis and rearrangement of cyclopropyl cation precursors in methanol to obtain a mixture of ring-opened and ring-expanded products .…”

Cuprate-Mediated Synthesis and Biological Evaluation of Cyclopropyl- and tert-Butylfarnesyl Diphosphate Analogs

“…If 3-cyclopropyl-3-desmethyl FPP ( 1 , 3-cpFPP) reacts via this pathway to give the allylic carbocation 2 , then the cyclopropylcarbinyl resonance isomer 3 may react with a nucleophile in the enzyme active site to give adduct 4 , which would result in the irreversible inactivation of PFTase. It is well established that cyclopropylcarbinyl cations such as 3 can react with nucleophiles to give homoallylic products such as 4 .…”

Silicon assisted diversified reaction of a β-silylmethylene malonate with dimethylsulfoxonium methylide

“…It is well established that cyclopropylmethyl halides, cyclobutyl halides and homoallyl halides are all in equilibrium in acid solutions and the mixture of products are often formed via delocalized cationic intermediate [77][78][79][80][81][82][83][84][85][86][87]. But, under present circumstances, this situation is unlikely.…”