The [5+5] route to the phenanthrene skeleton

Abstract

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.

Synthesis of highly substituted benzene ring systems through three-component coupling of enyne imines, Fischer carbene complexes, and electron-deficient alkynes

“…Diels-Alder reactions were initially performed at high concentration in toluene solvent using purified pyrrole-ketones at 0.1–0.3M concentration in refluxing toluene for 24 h. This process was high yielding for entries 1–2 and the TLC (silica gel) of the reaction showed no other mobile products. The reaction in entry 3 proceeded in lower yield, however the most obvious competing process, intramolecular Diels-Alder reaction resulting in 8 , 22 was not observed. The monosubstituted pyrrole system in entry 4 was completely unreactive to DMAD, regardless of whether the ketone or enol ether (expected to be more reactive) was employed in the Diels-Alder reaction event.…”