Stepwise 1,4-allyl migration

The pH-independent reaction of cyclopentadiene oxide 12 in water is clearly different from that of 13.97 This reaction yields 33% of 3-cyclopentenone, 35% of cis-2,4-pentadienal and 35% of a mixture of cis and trans 1,2- and 1,4-diols (Scheme 28). When the reaction is carried out in D20 instead of H20, no deuterium is incorporated into the ketone product. Thus, 1,2-hydrogen migration is required for this reaction just as it is in the rearrangement of arene oxides to phenols. The mechanisms of product formation in this reaction are not fully understood. The observation that the diol mixture is similar to that from the acid-catalyzed hydrolysis of 12 suggests that an allylic carbocation may be involved in the diol-forming reaction. Ketone (96) and dienal (97) products are potentially formed either by stepwise or concerted mechanisms, and there is insufficient evidence to rule out either one. There is a significant normal salt effect on this pH-independent... 

With respect to the stereochemistry, for an orbital symmetry allowed reaction inversion must accompany 1,3-migration (either antarafacial with respect to the allyl unit or inversion of the migrating center), or the reaction must proceed via nonconcerted pathways1181. As the [1,3] reaction of the thermolysis of syn- and ant/-7-(l-propenyl)norbornenol (9 and 12 respectively) produces 14 with high stereoselectivity (at 290 °C a 28 72 mixture of 11 and 14 from 9 and a 94 6 mixture from 12), a stepwise mechanism is probably operative via intermediates 10 and 13 formed by fragmentation and recombination1192. 

Calculations of the regio- and chemo-selectivities of C-H amination of silyl cyclopropenes by azodicarboxylates show that the initial Alder-ene reaction between the two reactants follows a stepwise mechanism and the subsequent allylic transposition proceeds via a concerted [1,3]-migration of hydrazodicarboxylate (Scheme 82). ... 

Tris- r-allyl cobalt also has catalytic activity and polymerizes butadiene causing hydrogen migration and giving S-methyl-hepta-l,3,6 trienes. A possible intermediate in this reaction is the complex 9.7, which has been isolated in a separate preparation [74]. Bis-7r-allyl cobalt reacts with butadiene in a novel stepwise reaction [73], viz. 

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