This page will summarize our studies in the area of carbene complex-alkyne coupling and is under construction. We recently published a review in the open access journal ARKIVOC on one aspect of this chemistry, [5+5] cycloaddition using o-alkynylbenzoyl derivatives and γ,δ-unsaturated carbene complexes.
We began the investigation into the coupling of conjugated alkynes and Fischer carbene complexes in the mid-1990’s in an effort to augment our studies in cyclopentenone formation based on cyclopropylcarbene complex alkyne coupling reactions. Closer examination of the reaction revealed that use of these coupling partners offered a fundamental advantage over traditional Fischer carbene complex alkyne couplings in that the molecular complexity in the reaction existed primarily in the alkyne, and alkyne synthesis is far “easier” than Fischer carbene complex synthesis. This approach could be extended to alternatives to the Dötz benzannulation reaction. That reaction was later extended to benzannulation reactions using dienyne systems.
In most cases, we were preparing the conjugated dienyne systems through Wittig reactions of conjugated enyne aldehyde systems. However, the enyne aldehyde precursors also featured a similar π-bond architecture, so why not try these as substrates. Reactions involving these system lead to furans. Replacement of the central alkene group with a benzene ring leads to isobenzofuran systems, which are too unstable to isolate. If a Diels-Alder trap is incorporated into the system, then the isobenzofuran intermediate can be trapped. The dienophile is can be tethered to the alkyne or to the carbonyl group, and in some cases can simply be added to the reaction mixture. The most important system developed however is the net [5+5] cycloaddition system, which involves tethering the dienophile to the carbene complex.