Gold-Catalyzed Dearomative Spirocyclization of Aryl Alkynoate Esters

Abstract

Aryl alkynoate esters undergo gold-catalyzed spirocyclization under mild conditions, affording spirolactones in high yields. This approach obviates the need for stoichiometric halogenating reagents typically employed for alkyne activation in related transformations. Water was found to play a critical role in governing the product selectivity. Anhydrous conditions lead selectively to coumarin products, as has previously been observed for aryl alkynoate esters, while the addition of 1 equiv of water leads selectively to spirocycle formation.

Gold(I)-Catalyzed Activation of Alkynes for the Construction of Molecular Complexity

“…342b , 344b , 354 It has been recently reported that the same substrates under the same reaction conditions swapping from anhydrous to wet solvent undergo a gold(I)-catalyzed spirocyclization under mild conditions, giving spirolactones 409 in high yields. 355 Spiro[4.5]cyclohexadienones have been also obtained by a gold(I)-catalyzed carbocyclization of phenols with a terminal alkyne via intramolecular ipso -Friedel–Crafts. 356 Aryl alkynylphosphonates also undergo intramolecular gold(I)-catalyzed hydroarylation to give phosphacoumarins.…”

Catalytic Dearomative Spirocyclization via Gold Carbene Species Derived from Ynamides: Efficient Synthesis of 2‐Azaspiro[4.5]decan‐3‐ones

“…This electron‐deficient carbene species undergoes nucleophilic attack from the ipso position to give spirocycle B . The resulting spirocyclic compound B reacts with water to give C . The presence of a catalytic amount of quinoline may promote this hydrolytic demethylation step by increasing the basicity .…”

“…These resultsm ean that Cl of LAuCl was replaced by OH from water,and LAu(OH) would be an activecatalyst. [10,11] We next added ac atalytic amount of quinoline as a basic additive and the isolated yield improved to 85 % (entry 14). [12] The base probably captured the in situ-generated hydrogen chloride.…”

“…Regarding the mechanism, we propose the formation of acyl gold carbene species A prepared from ynamide 1 and Au I complex with aN HC ligand as the initial step (Scheme 4). [16] This electron-deficient carbene species undergoes nucleophilic attack from the ipso position to give spirocycle B.T he resulting spirocyclic compound B reacts with water to give C. [11] The presenceo facatalytic amounto fq uinoline may promote this hydrolyticd emethylation step by increasing the basicity. [12] Finally,p rotodemetallation of C provides desired spirocyclic compound 2 and regenerates the gold catalyst.…”

Silica Gel as a Promoter of Sequential Aza‐Michael/Michael Reactions of Amines and Propiolic Esters: Solvent‐ and Metal‐Free Synthesis of Polyfunctionalized Conjugated Dienes

“…Phenyl propiolate ( 2 f ) was obtained according to the procedure given for the synthesis of aryl alkynoate esters . A solution of DCC ( N,N′ ‐dicyclohexylcarbodiimide) (520.0 mg, 2.5 mmol) in CH 2 Cl 2 (2 mL) was added to a solution of propiolic acid (197.0 mg, 2.8 mmol) in CH 2 Cl 2 (2 mL) at 0 °C.…”