Electrocyclic Ring Opening of Cyclopropyl Ions and Radicals

Electrocyclic Ring Opening of Cyclopropyl Ions and Radicals 

Cyclopropyl ions and radicals (23) can undergo conversion to allyl (24) by typical electrocyclic ring opening processes we have carried out calculations for ring opening by both conrotatory and disrotatory paths. Table 5 shows calculated activation energies for the various processes. 

Compound Calculated activation energy for ring opening (kcal/mole) disrotatory conrotatory  

Note that we predict ring opening of the cyclopropyl cation to require activation this at first sight seems to be at variance with evidence that rearrangement occurs as a concerted process in the solvolysis of cyclopropyl esters and indeed acts as a driving force 44). Moreover the evidence shows very clearly that this is so only for one of the possible disrotatory processes, i.e. that indicated in 25  

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E. Electrocyclic Ring Opening of Cyclopropyl Ions and Radicals... 

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