[1,4] migratioms in acid catalyzed rearrangements of β-naphthalenones

Periselectivity between the [1,4] and [3,3] thermal sigmatropic rearrangements of 2-allyloxypyridine N-oxides

“…30%). They conclude 7*8 that the [ 1,2] and [1,4] rearrangements both proceed by a non-concerted radical + radical anion cleavagerecombination mechanism. The possible role of a 'radical concerted' process in the Wittig [1,2] rearrangement has been carefully explored by Garst and Smith."…”

“…Survey of [ 1,4] Sigmatropic Rearrangements.-Thermal [ 1,4] sigmatropic rearrangements may be categorised into three classes depending upon the intermediate, which may be cationic, anionic, or dipolar (ylide or betaine). Cationic [1,4] sigmatropic rearrangements are 4-electron processes and normally proceed in the [la,4,] mode which is associated with inversion of configuration at the terminus of the migrating group. In contrast, anionic and dipolar [ 1,4] sigmatropic rearrangements involve 6-electron [ lS,4J processes associated with retention of configuration at the terminus of the migrating group.…”

“…Cationic [1,4] sigmatropic rearrangements are 4-electron processes and normally proceed in the [la,4,] mode which is associated with inversion of configuration at the terminus of the migrating group. In contrast, anionic and dipolar [ 1,4] sigmatropic rearrangements involve 6-electron [ lS,4J processes associated with retention of configuration at the terminus of the migrating group.…”

“…The inversion of configuration of cationic [ 1,4] sigmatropic shifts constrained to proceed suprafacially has been convincingly demonstrated in the rapid equilibration of protonated bicyclohexenones and the degenerate migration of the cyclopropane ring around the periphery of the 5-membered allylic cation during the [1,4] sigmatropic rearrangement of hexamethylbicyclo[3.l.0]hexenyl cation^.^ Formal [ 1,4] migrations of crotyl and benzyl groups have been observed4 in the acid catalysed reaction between 1,l -disubsti tuted P-naphthalenones and acetic anhydride-sulphuric acid. In a detailed investigation of the acid-catalysed rearrangement of various 4-allylcyclohex-2-en-ols, Schmid has demonstrated that [3,4] sigmatropic rearrangements involving cyclohexadienyl cations do occur, whereas [ l,4] sigmatropic rearrangements occur relatively infrequently. ' Anionic sigmatropic rearrangements are exemplified by the Wittig rearrangement of ethers and the corresponding basecatalysed rearrangements of thioethers.…”

“…' Anionic sigmatropic rearrangements are exemplified by the Wittig rearrangement of ethers and the corresponding basecatalysed rearrangements of thioethers. With allyl ethers, competition between the [1,2] and [1,4] sigmatropic rearrangements is possible and this aspect has been examined by several Felkin and Frajerman ' have shown that the [ 1,2] and [ 1,4] rearrangements of S-ally1 1-phenylethyl ether both proceed with predominant retention of configuration and approximately the same extent of racemisation (ca. 30%).…”