This account describes the historical development of the coupling of γ,δ-unsaturated Fischer carbene complexes and o-alkynylbenzaldehydes, which directly affords hydrophenanthrene ring systems in a process where each reactant contributes five carbons to the newly-formed bicyclo[4.4.0]decane ring system. The process has been termed net [5+5] cycloaddition. Use of the reaction to produce various medicinally important natural products and/or their parent ring systems is discussed.

Three-component coupling of Fischer carbene complexes, enyne aldehyde hydrazones, and electron-deficient alkynes leads to simple benzoate derivatives in a process involving the formation of an N-aminopyrrole derivative, Diels-Alder reaction, and nitrene extrusion. The products are readily converted into isoquinolones through reaction with primary amines. The reaction proceeds best with highly substituted and electron-rich pyrroles even though these are the sterically least favorable substrates, and this reactivity trend is supported by a computational study.