Gold-Katalyse: hochfunktionalisierte Cyclopentadienderivate durch intermolekulare Cyclisierung von Inamiden und Propargylcarboxylaten

Gold-Catalyzed Reaction of Propargyl Esters and Alkynylsilanes: Synthesis of Vinylallene Derivatives through a Twofold 1,2-Rearrangement

The reaction of propargyl esters with alkynylsilanes under gold catalysis provides vinylallene derivatives through consecutive [1,2]‐acyloxy/[1,2]‐silyl rearrangements. Good yields, full atom‐economy, broad substrate scope, easy scale‐up and low catalyst loadings are salient features of this novel transformation. Density Functional Theory (DFT) calculations suggest a reaction mechanism involving initial [1,2]‐acyloxy rearrangement to generate a gold vinylcarbene intermediate which upon regioselective attack of the alkynylsilane affords a vinyl cation which undergoes a type II‐dyotropic rearrangement involving the silyl group and the metal fragment. Preliminary results on the enantioselective version of this transformation are also disclosed.

Keteniminium-Driven Umpolung Difunctionalization of Ynamides

A three-component Pd-catalyzed coupling of ynamides, aryl diazonium salts, and aryl boronic acids for the synthesis of novel triaryl-substituted enamides is described. This transformation represents the first example of an umpolung regioselective unsymmetrical syn-1,2-diarylation/aryl-olefination of ynamides. The aryl moieties of the diazonium salt (electrophile) and boronic acid (nucleophile) are explicitly incorporated in the electrophilic α- and nucleophilic β-position, respectively, of the ynamide, resulting in a single isomer of the N-bearing tetrasubstituted olefin. The scope is broad (68 examples), showing excellent functional-group tolerance. DFT calculations substantiate the rationale of the mechanistic cycle and the regioselectivity. The chemoselectivity and synthetic potential of the enamide products were also studied.

Acyl Migration versus Epoxidation in Gold Catalysis: Facile, Switchable, and Atom-Economic Synthesis of Acylindoles and Quinoline Derivatives

We report a switchable synthesis of acylindoles and quinoline derivatives via gold-catalyzed annulations of anthranils and ynamides. α-Imino gold carbenes, generated in situ from anthranils and an N,O-coordinated gold(III) catalyst, undergo electrophilic attack to the aryl π-bond, followed by unexpected and highly selective 1,4- or 1,3-acyl migrations to form 6-acylindoles or 5-acylindoles. With the (2-biphenyl)di-tert-butylphosphine (JohnPhos) ligand, gold(I) carbenes experienced carbene/carbonyl additions to deliver quinoline oxides. Some of these epoxides are valuable substrates for the preparation of 3-hydroxylquinolines, quinolin-3(4H)-ones, and polycyclic compounds via facile in situ rearrangements. The reaction can be efficiently conducted on a gram scale and the obtained products are valuable substrates for preparing other potentially useful compounds. A computational study explained the unexpected selectivities and the dependency of the reaction pathway on the oxidation state and ligands of gold. With gold(III) the barrier for the formation of the strained oxirane ring is too high; whereas with gold(I) this transition state becomes accessible. Furthermore, energetic barriers to migration of the substituents on the intermediate sigma-complexes support the observed substitution pattern in the final product.

Synthesis of 3-Amino-1-benzothiophene-1,1-diones by Alkyne Directed Hydroarylation and 1/N→3/C-Sulfonyl Migration

A completely regioselective and highly stereoselective palladium-catalyzed intramolecular hydroarylation of arenesulfonyl ynamines to benzothiazoles was developed. The presence of an electron-withdrawing group on the triple bond of the sulfonyl ynamine was crucial for the success of the reaction and our mechanistic studies suggest an alkyne-directed 5-exo-dig cyclization pathway. The products easily underwent photoinduced rearrangement to 3-amino-1-benzothiophene-1,1-diones (up to 35 % yields after two steps).

Gold(I)-catalyzed 1,2-acyloxy migration/[3+2] cycloaddition of 1,6-diynes with an ynamide propargyl ester moiety: highly efficient synthesis of functionalized cyclopenta[b]indoles

A gold-catalyzed cycloisomerization of 1,6-diynes containing an ynamide propargyl ester or carbonate moiety has been developed that provides an attractive route to a diverse-substituted 3-acyloxy-1,4-dihydrocyclopenta[b]indoles. Mechanistic studies indicate that the reaction likely proceeds through a competitive 1,2-OAc migration followed by [3+2] cycloaddition of the vinyl gold-carbenoid intermediate with the pendant triple bond. The synthetic utility of the obtained cyclopenta[b]indole products was demonstrated by their efficient transformations by deprotection or double-bond isomerization reactions.

1,2-N-migration in a gold-catalysed synthesis of functionalised indenes by the 1,1-carboalkoxylation of ynamides

Unique α-hemiaminal ether gold carbene intermediates were accessed by a gold-catalysed 1,1-carboalkoxylation strategy and evolved through a highly selective 1,2-N-migration. This skeletal rearrangement gave functionalised indenes, and isotopic labelling confirmed the rare C–N bond cleavage of the ynamide moiety. The effect of substituents on the migration has been explored, and a model is proposed to rationalise the observed selectivity.

Gold-catalyzed [2+2+1] cycloaddition of 1,6-diyne carbonates and esters with aldehydes to 4-(cyclohexa-1,3-dienyl)-1,3-dioxolanes

A synthetic method to stereoselectively prepare 4-(cyclohexa-1,3-dienyl)-1,3-dioxolanes in good to excellent yields by gold(I)-catalyzed [2+2+1] cycloaddition of 1,6-diyne carbonates and esters with aldehydes is described. The cascade process involves 1,2-acyloxy migration followed by cyclopropenation and cycloreversion. This leads to an unprecedented [2+2+1] cycloaddition of the resulting alkenylgold carbenoid species, examples of which are extremely rare, with two aldehyde molecules at catalyst loadings as low as 1 mol %. The usefulness of this cycloisomerization chemistry was further demonstrated by the transformation of one example to the corresponding phenol.