Assembly of Complex 1,4-Cycloheptadienes by (4+3) Cycloaddition of Rhodium(II) and Gold(I) Non-Acceptor Carbenes.

The formal (4+3) cycloaddition of 1,3-dienes with Rh(II) and Au(I) non-acceptor vinyl carbenes, generated from vinylcycloheptatrienes or alkoxyenynes, respectively, leads to 1,4-cycloheptadienes featuring complex and diverse substitution patterns, including natural dyctiopterene C' and a hydroxylated derivative of carota-1,4-diene. A complete mechanistic picture is presented, in which Au(I) and Rh(II) non-acceptor vinyl carbenes were shown to undergo a vinylcyclopropanation/Cope rearrangement or a direct (4+3) cycloaddition that takes place in a non-concerted manner.

On the Structure of Intermediates in Enyne Gold(I)-Catalyzed Cyclizations: Formation of trans-Fused Bicyclo[5.1.0]octanes as a Case Study.

The nature of cyclopropyl gold(I) carbene-type intermediates has been reexamined as part of a mechanistic study on the formation of cis- or trans-fused bicyclo[5.1.0]octanes in a gold(I)-catalyzed cascade reaction. Benchmark of DFT methods together with QTAIM theory and NBO analysis confirms the formation of distinct intermediates with carbenic or carbocationic structures in the cycloisomerizations of enynes.

Acetylene as a Dicarbene Equivalent for Gold(I) Catalysis: Total Synthesis of Waitziacuminone in One Step.

The gold(I)-catalyzed reaction of acetylene gas with alkenes leads to (Z,Z)-1,4-disubstituted 1,3-butadienes and biscyclopropanes depending on the donor ligand on gold(I). Acetylene was generated in situ from calcium carbide and water in a user-friendly procedure. Reaction of acetylene with 1,5-dienes gives rise stereoselectively to tricyclo[5.1.0.02,4 ]octanes. This novel double cyclopropanation has been applied to the one step total synthesis of the natural product waitziacuminone from acetylene and geranyl acetone.

Diastereospecific Gold(I)-Catalyzed Cyclization Cascade for the Controlled Preparation of N- and N,O-Heterocycles.

The reaction of oxime-tethered 1,6-enynes with a cationic gold(I) catalyst demonstrates a great potential for the synthesis of a range of heterocycles in a diastereospecific fashion. The control of the configuration of the oxime and the alkene of the enyne moiety is the key to selectively obtain dihydro-1,2-oxazines, isoxazolines or dihydropyrrole-N-oxides as single diastereoisomers. As supported by DFT calculations, these cascade reactions proceed stepwise, by the intramolecular addition of the O or N atom of the oxime onto cyclopropyl gold(I) carbene intermediates. In this study, a rare [3,3]-sigmatropic rearrangement of nitrones is also observed.