Gold‐Catalyzed Rearrangements: Reaction Pathways Using 1‐Alkenyl‐2‐alkynylcyclopropane Substrates

Mechanistic Studies on the Rearrangement of 1‐Alkenyl‐2‐alkynylcyclopropanes: From Allylic Gold(I) Cations to Stable Carbocations

“…We have recently studied the reactivity of a specific class of 1,5‐enynes, that is, the alkynylcyclopropanes 1 , which undergoes a gold‐catalyzed rearrangement to the alkynylcyclohexadienes 2 and 3 (Scheme ) 5. At that stage, a tentative pathway for the formation of 2 and 3 involving a 3‐ exo‐dig attack via the intermediates I and I′ , respectively, was suggested.…”

Mechanistic Studies on the Rearrangement of 1‐Alkenyl‐2‐alkynylcyclopropanes: From Allylic Gold(I) Cations to Stable Carbocations

“…The relative energies found for B going to either TS1 or TS3 (23.5 kcal mol À1 , in both cases) indicate that an equilibrium between C and A is feasible, as it was proposed to explain the formation of isomers. [5] Conversely, the earlier postulated 3-exo-dig nucleophilic attack (Scheme 2) seems to be less likely as the calculated structure for the corresponding transition state is higher in energy than TS1 (+ 17.8 versus + 6.2; see the Supporting Information for the complete calculated pathway).…”

“…[4] We have recently studied the reactivity of a specific class of 1,5-enynes, that is, the alkynylcyclopropanes 1, which undergoes a gold-catalyzed rearrangement to the alkynylcyclohexadienes 2 and 3 (Scheme 2). [5] At that stage, a tentative pathway for the formation of 2 and 3 involving a 3-exo-dig attack via the intermediates I and I', respectively, was suggested. The formation of 2 and 3 was justified assuming an isomerization of 1 through a reversible 6-endo-dig attack of the olefin involving intermediate II, a formal allylic gold(I) cation.…”

“…Preliminary indications on the participation of II were gained by its trapping with alcohols as nucleophiles, [5] and led to the isolation of the compounds 4 and 5 (see Scheme 3) depending to the size of the alcohol. [6] Moreover, we have also found that the outcome in the reaction of the alkynylcyclopropane 1 a and MeOH can be correlated with the percent buried volume (%V bur ) of the gold complexes (Scheme 3).…”

Gold‐Catalyzed Functionalization of Unactivated C(sp3)H Bonds by Hydride Transfer Facilitated by Alkynylspirocyclopropanes

“…As part of our research into the synthesis and reactivity of alkynylcyclopropane derivatives, [9,10] we have recently reported the synthesis of spiro [2,4]heptane derivatives 1 whose particular structure makes them amenable for use in investigations of new metal-catalyzed processes. [11] These compounds have severe geometrical restrictions that place an inactive methylene group close to the alkyne moiety.…”