Sequential rearrangements via bridged carbocations

Lewis Acid-Mediated Cycloaddition of Methylenecyclopropanes with Aldehydes and Imines: A Facile Access to Indene, THF, and Pyrrolidine Skeletons via Homoallylic Rearrangement Protocol

“…The aryl migration in cation F (for arylaldehydes), which has been clearly indicated by the deuterium-labeling experiment, takes place in the presence of Lewis acid to produce another cation G , which gives intermediates H and I . The proton migration of I finally affords product 3 . On the basis of this proposed mechanism, the results shown in Tables and can be rationalized as follows.…”

A novel route towards formylated 1,3-dithiole-2-thiones via an unprecedented allylic 1,4-diol rearrangement

“…The involvement of a phenonium intermediate in aryl shifts has been seen previously. 7 Theoretical studies have shown that there is significant stabilisation of the phenonium ion through back-bonding from the ethylene unit of spirocyclopropylbenzenium species. 8 However, we propose a spirocyclopentylbenzenium intermediate 12 in Scheme 2, which can only be stabilised by the methoxy unit.…”

Electrophile-Induced Ring Expansions of β-Lactams toward γ-Lactams

“…After ring expansion, the bromide will attack from the same side where the bromomethyl group is formed, because it is at this side that the bromide is formed after the ring expansion. The same concepts concerning external ion pair return were already proven to be responsible for the stereochemical control of “memory effects”. − This term is used in reactions of carbocations in which the latter “remember” how they were formed before they go on to give the second step. Also in these cases, counterions attacked the rearranged carbocations from the side from which they were expelled (during ionization).…”