Cyclopropanes epoxide ring opening

The Lewis acid rearrangement of epoxides is a valuable tool for the stere-oseleetive construction of cyclopropane moieties. Lambert has described a Lanthanum-catalyzed olefin cyclopropanation through an intramolecular methylene transfer (Scheme 5.31) [103]. According to the authors, the sequence involves intramolecular epoxide ring-opening of 88 followed by a semi-pinacolic... 

Narjes, F., Bolte, O., Icheln, D., Konig, W.A., and Schaumatm, E. (1993) Synthesis of vinyl-cyclopropanes by intramolecular epoxide ring opening application for an enantioselective synthesis of dictyopterene-A./. Org. Chem.. 58, 626-632. 

While generation of a Mn(V)oxo salen intermediate 8 as the active chiral oxidant is widely accepted, how the subsequent C-C bond forming events occur is the subject of some debate. The observation of frans-epoxide products from cw-olefins, as well as the observation that conjugated olefins work best support a stepwise intermediate in which a conjugated radical or cation intermediate is generated. The radical intermediate 9 is most favored based on better Hammett correlations obtained with o vs. o . " In addition, it was recently demonstrated that ring opening of vinyl cyclopropane substrates produced products that can only be derived from radical intermediates and not cationic intermediates. ... 

A suspension of thallium (III) nitrate in hexane reacts with epoxides to give the corresponding -hydroxy nitrate esters in good yield. The same reagent in acetonitrile has been used to synthesize a-nitratoketones from substituted acetophenones, 1,2-dinitrate esters from alkenes, and 1,3-dinitrates from ring-opening nitration of cyclopropanes. ... 

Carbanions. These add to the C-3 position of (5)-(l), affording epoxides (3) after intramolecular displacement of the tosylate group and in situ ring closure of the ring-opened intermediate (eq 4). Deprotonation of oxirane (3) leads to rearrangement to cyclopropane derivatives. ... 

Previous work by Jeger and his coworkers has studied the photoreactivity of y.5-epoxy enones. More recent work by Ishii et aJ has examined the photochemical reactivity of the related nitriles (145) and (146). The direct irradiation of (145) brings about isomerization by ring opening of the cyclopropane to afford (147) as the major product. This is accompanied by the cyclopropenyl nitrile (148) presumably formed via a carbene intermediate. Triplet sensitized irradiation of (145) only brings about trans-cis isomerization. The epoxide (149) is also photoreactive and direct irradiation affords the products (150) - (156) either by the intermediacy of an ylide (157) or a carbene (156). ... 

Small rings (epoxides, cyclopropanes) Biphenyl Fast opening of the anion radical Fast cleavage of C— N and C—S [39, 45]... 

Jacobsen reported in 1990 that Mnm complexes of chiral salen ligands (41) were the most efficient catalysts available for the enantioselective epoxidation of alkyl- and aryl-substituted olefins.118 This stimulated a rapid development in the chemistry and applications of chiral SB complexes, which offer promising catalytic applications to several organic reactions, such as enantioselective cyclopropanation of styrenes, asymmetric aziridination of olefins, asymmetric Diels-Alder cycloaddition, and enantioselective ring opening of epoxides.4,119... 

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