Furst-Plattner effect

The observation that the methylative ring opening of the cis-epoxide 56 did not, according to the Furst-Plattner rule, take place at C3 (trans-diaxial process) but at C4 to provide 58 could be explained by the less stable but chelation-supported 56a. To prove this effect, the reaction was reran but this time in the presence of a crown ether to sweep all the cations from the solution. 

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