English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Zendy Plus

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Zendy Tools

Zendy Open

A series of 12 alkynes has been protonated with FSO3H-SbFs (magic acid) in SO2 or S02CIF solution under stable ion conditions. Whereas the formation of oligomeric products was observed at -78 OC, allyl cations were formed in high yields at higher temperatures. In many cases this way of preparing allyl cations is superior to other methods. While alkynes, which are branched in the a position to the triple bond, underwent rearrangements to allyl cations after protonation in SO2 at -20 OC, the corresponding reactions of the unbranched systems demanded higher temperatures. Only the sterically crowded di- tert-butylacetylene rearranged to stereoisomeric allyl cations upon protonation even at -78 OC. The nonequilibrium nature of the protonation step and the intermediacy of vinyl cations was demonstrated by deuterium labeling. Whereas trivalent alkyl cations have been recognized as reactive intermediates since Ingold's definition of SN 1 reac- tions2 and have been extensively studied as long lived species within the last 15 years,3 evidence for the existence of vinyl cations4 has proved to be more elusive. Indeed, the low reac- tivity of vinyl halides under SN~ conditions has suggested that vinyl cations are not formed as reactive intermediates. During the last ten years, however, extensive studies on the solvolysis of vinyl derivatives, the plurality of which have been a-phenyl substituted, have provided indirect evidence for the inter- mediacy of vinyl cation^.^ Recently, the reaction of a-aryl vinyl fluorides with SbFS has been reported to yield vinyl cations as stable species in low nucleophilic media by both Hanack6a and Masamune.6b Discrepancies of results and the question of whether real vinyl cations were indeed observed, however, remain to be resolved.

journal of the american chemical society

Stable Carbocations. 198. Formation of Allyl Cations via Protonation of Alkynes in Magic Acid Solution. Evidence for 1,2-Hydrogen and Alkyl Shifts in the Intermediate Vinyl Cations