Gold Catalysis: Highly Functionalized Cyclopentadienes Prepared by Intermolecular Cyclization of Ynamides and Propargylic Carboxylates

Gold‐Catalyzed Intramolecular Tandem Cyclization of Indole‐Ynamides: Diastereoselective Synthesis of Spirocyclic Pyrrolidinoindolines

“…We therefore started to explore Au‐catalyzed annulation for the synthesis of product 7 from ynamide 6 . We first tested [(IPr)AuCl]/AgNTf 2 (IPr=1,3‐bis(diisopropylphenyl)imidazol‐2‐ylidene) as a catalyst, and to our delight, the desired product 7 was obtained in 60 % yield when the reaction was carried out in DCM at 25 °C for 30 min. The structure of 7 was confirmed by 2D‐NMR spectroscopy, and later supported by an X‐ray crystal structure of its derivative 9 q (Table , see the Experimental Section).…”

Alkyne Versus Ynamide Reactivity: Regioselective Radical Cyclization of Yne‐Ynamides

“…Importantly,a ll these transformations involve nucleophilic attack by the ynamide motif (via an oxo-metal carbene [2] /ketene N,O-acetal) on the alkyne scaffold (Scheme 1a). [5] Aw orthwhile endeavor would thus be to unravel ar adical-mediated cyclization [6] of ynetethered ynamides,with the prediction of ap referred radical attack on the alkyne rather than the inherently polarized ynamide (path II over path I; Scheme 1b), which, to the best of our knowledge,isunprecedented. [5] Aw orthwhile endeavor would thus be to unravel ar adical-mediated cyclization [6] of ynetethered ynamides,with the prediction of ap referred radical attack on the alkyne rather than the inherently polarized ynamide (path II over path I; Scheme 1b), which, to the best of our knowledge,isunprecedented.…”

“…[3,4] In contrast, synthetic techniques that are based on reversing the usual reactivity of ynamides over alkynes have been only rarely reported. [5] Aw orthwhile endeavor would thus be to unravel ar adical-mediated cyclization [6] of ynetethered ynamides,with the prediction of apreferred radical attack on the alkyne rather than the inherently polarized ynamide (path II over path I; Scheme 1b), which, to the best of our knowledge,isunprecedented. Thus,radical-triggered 6endo-/5-exo-cyclization of the alkyne to the ynamide would result in the formation of 6-or 5-membered N-heterocycles, respectively (path II, Scheme 1b).…”

Synthetic Routes towards Multifunctional Cyclopentadienes

“…As an alternative, a stepwise reaction in which the ynamide nucleophilically attacks the electron‐poor carbene carbon to form a keteniminium intermediate was proposed. Subsequent ring closure and elimination of the catalyst would also deliver the same final Cp . Even though the group reported 21 different Cps, the structural variety was not particularly expansive, hinting at certain intrinsic limitations of the procedure.…”