Furst— Plattner rule

Nucleophilic attack on oxirane carbon usually proceeds with inversion of configuration (Scheme 44) as expected for SN2 reactions, even under acid conditions (Scheme 45). Scheme 45 also illustrates the fact that cyclohexene oxides open in a /rans-diaxial manner this is known as the Furst-Plattner rule (49HCA275) and there are very few exceptions to it. 

The Furst-Plattner Rule the onium ion may be exerted —in addition to the factors already discussed (factor 1 see Fig-... 

Strong preference for chair over twist boat development appears to be general, and is often referred to as the rule of diaxial opening or the Furst-Plattner rule. Twist boat processes can be encouraged by suitable substitution, but in the absence of such special features there are no known examples of cyclohexene oxides which give appreciable amounts of twist boat opened products (sometimes called diequatorial-opening products). The lone apparent exception has been shown to be an artifact caused by an impurity. 

On nucleophilic attack, the epoxide ring opens according to the Furst-Plattner rule, with the formation of the di-axial derivative, because the pyranoid rings in the frons-linked derivatives (98) and (99) are completely fixed and the cfs-linked derivatives (100) and (101) are fixed to a considerable extent in the Cl form. (The corresponding members of the L series belong to the 1C form ) The 2-deoxy derivatives are prepared by the mercaptal method, and also, more easily, by direct reduction of the anhydro derivatives (98) and (100) with lithium aluminum hydride. Only the riho and xylo configurations, (102) and (104), are accessible (X = H), but these are obtained in very good yield. This... 

All produets had eonfigurations as predieted by the Furst Plattner rule, whieh implies that fission of the benzylidene group had to take plaee after aziridine-ring cleavage. 

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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