Cyclopropyl cation electrocyclic formation

The most simple electrocyclic reaction involving a 2k electron system is the formation of an alkyl cation from a cyclopropyl cation... 

If, however, there is a strongly cation-stabilizing substituent at the reaction center, cyclopropanes 10 are observed as byproducts, or even predominant products, in addition to allylic compounds 8. A two-step mechanism with electrocyclic opening of stabilized cyclopropyl cation 9 has been proposed for the formation of allylic products 8 from cyclopropanes 6. In at least one case 9 was unequivocally observed by spectroscopic means. The 1-ferrocenyl-l-cyclopropyl cation has been observed in superacidic solution at — 40 C by H and C... 

Formation of allylic products is characteristic of solvolytic reactions of other cyclopropyl halides and sulfonates. Similarly, diazotization of cyclopropylamine in aqueous solution gives allyl alcohol. The ring opening of a cyclopropyl cation is an electrocyclic process of the 4n + 2 type, where n equals zero. It should therefore be a disrotatory process. There is another facet to the stereochemistry in substituted cyclopropyl systems. Note that for a d5-2,3-dimethylcyclopropyl cation, for example, two different disrotatory modes are possible, leading to conformationally distinct allyl cations. 

On the other hand, cation formation by decarboxylation of an acyloxonium cation RC02+ is supported by the partial stereospecificity observed in the electrolysis of cis- and trans-bicyclo [3.1.0] hexane-3-carboxylic acid 2°5 and the electrocyclic ring opening in the anodic oxidation of 3-methyl-2-phenylcyclopro-panecarboxylate (22, 23) to cyclopropyl methyl ether (24, 25) and allylic ethers (26, 27) (Eq. (97)) 206). 

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