Non-Concerted Cope Rearrangement

Cope Reaction Families: To Be or Not to Be a Biradical

“…This rule follows the spirit of previous theoretical studies, , which stated that biradical intermediates are present when radical-stabilizing substituents (phenyl, vinyl, cyano) are connected to the 2- and/or 5-positions of the 1,5-hexadiene moiety, and also experimental findings.…”

The thermolytic behaviour of hexa-1,5-diene-units incorporated in a stellane and twistbrendane skeleton. A quest for a stepwise Cope rearrangement

“…Arguments from experiment for a stepwise mechanism are due to the investigations of 11 and 21 in the gas-phase. 11 All the evidence in these investigations (trapping of intermediates with O 2 ) and similarity of kinetic data between 11 and 21 support the formation of a diradical intermediate. By the same token we interpret the similarity of the kinetic data obtained for 11 in solution and in the gas-phase that the rate determining step is the bond cleavage of one of the central C-C σ-bonds of the stellane skeleton.…”

“…Cope rearrangement of 11 to 16. Parts of the results have already been published elsewhere 11 (see also Table 4 and Fig. 2).…”

“…The activation parameters measured for o-stelladiene 11 in d 8 -toluene compare very well to those previously obtained in the gas-phase (Table 2). 11 This similarity suggests that the rearrangement of 11 follows the same mechanism in both the gas-phase and in solution. As has been deduced from the comparison to the ring opening reaction of the isomeric p-stelladiene 21, the rearrangement of 11 is likely to occur via a two step mechanism.…”

3-Aza-Cope Rearrangement of Quaternary N-Allyl Enammonium Salts. Stereospecific 1,3 Allyl Migration from Nitrogen to Carbon on a Tricyclic Template

“…By contrast, the rearrangement of 13 or 21 required heating in the range of 50−100 °C and also resulted in some homolytic dissociation, as evidenced by the formation of oxidized byproduct 17 and nonconcerted rearrangement products 15b or 22b . This minor amount of nonconcerted mechanism (via pathway C in Scheme ) might be facilitated by a combination of a nitrogen atom in the aza-Cope array, an aromatic substituent, and the aforementioned torsional strain …”