Gold(I)-Catalyzed Rautenstrauch/Hetero-Diels-Alder/Retro-aza-Michael Cascade Reaction for the Synthesis of α-Hydrazineyl-2-cyclopentenones.

A one-pot synthesis of ring-fused, α-hydrazineyl-2-cyclopentenone derivatives is achieved by a gold(I)-catalyzed Rautenstrauch/hetero Diels-Alder/ring opening tandem reaction of suitable propargyl esters. By mixing the latter with a dialkylazodicarboxylate in the presence of a gold(I) catalyst, the 1,2-acyloxy migration/cyclization process (Rautenstrauch reaction) leads to cyclopentadienyl ester intermediates which are trapped by the heterodienophile present in situ. This provides strained intermediates which spontaneously undergo highly regioselective ring opening by a retro aza-Michael reaction promoted by the gold(I) catalyst, eventually yielding the target compounds.

Synthesis of 5-Hydrazino-2-cyclopentenone Derivatives by a Gold(I)-Catalyzed Cycloisomerization/Hetero-Diels-Alder/Ring-Opening Tandem Reaction of Enynyl Acetates.

A highly efficient, one-pot synthesis of ring-fused 5-hydrazino-2-cyclopentenone derivatives is achieved by a gold(I)-catalyzed cycloisomerization/hetero-Diels-Alder/ring-opening tandem reaction of suitable enynyl acetates. By mixing the latter with a dialkylazodicarboxylate in the presence of a gold(I) catalyst, the 1,3-acyloxy migration/Nazarov cyclization process leads to dienyl acetate intermediates which are trapped by the heterodienophile present in situ. This provides strained intermediates which undergo highly regioselective ring opening by a retro aza-Michael reaction promoted by traces of water, eventually yielding the target compounds.

Gold(I)-Catalyzed Cycloisomerization/Hetero-Diels-Alder Reaction/Ring Opening Cascade to Functionalized Cyclopentadienes.

Six- and seven-membered ring-fused, functionalized cyclopentadienes can be obtained in moderate to excellent yields by a cascade process entailing the Au(I)-catalyzed propargyl Claisen rearrangement/Nazarov cyclization of propargyl vinyl ethers, the hetero-Diels-Alder reaction with dialkylazodicarboxylates, and the spontaneous conversion of cycloaddition products into cyclopentadienes by a highly regioselective cleavage of a C-N bond. Depending on the treatment of the crude reaction mixtures, two types of products can be obtained: cyclopentadienes with pendant hydrazine and aldehyde moieties that intramolecularly react to form hemiaminals are obtained in 43-52% overall yields when the crude reaction mixtures are left over KCO in a DCM solution. Instead, by reducing the aldehyde group just after addition of the heterodienophile, the regioselective C-N bond cleavage generates the corresponding cyclopentadienes bearing a hydrazine and an alcohol appendage in excellent yields (66-82%) over four steps, all in one pot.

Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom.

The tandem gold(I)-catalyzed rearrangement/Nazarov reaction of enynyl acetates in which the double bond is embedded in a piperidine ring was computationally and experimentally studied. The theoretical calculations predict that the position of the propargylic acetate substituent has a great impact on the reactivity. In contrast to our previous successful cyclization of the 2-substituted substrates, where the nitrogen favors the formation of the cyclized final product, the substitution at position 3 was computed to have a deleterious effect on the electronic properties of the molecules, increasing the activation barriers of the Nazarov reaction.