Nucleophilic Addition/Double Cyclization Cascade Processes between Enynyl Fischer Carbene Complexes and Alkynyl Malonates

Abstract

Two new selective cascade processes for enynyl Fischer carbene complexes 1 are described in their reaction with alkynyl malonates. When carbene complexes 1 react with the sodium enolate of homopropargyl malonates 3 a consecutive Michael type addition/cyclopentannulation/6-exo cyclization takes place leading, in a regio and stereoselective way, to n/5/6 angular tricyclic compounds 5. Furthermore, when propargylic malonates are used, a delayed protonation of the reaction mixture allows intermediate 1,4addition adduct Ia to evolve through a 5-exo cyclization, consisting in an intramolecular nucleophilic attack from the central carbon of the allenylmetallate over the triple CC bond. Further spontaneous cyclopentannulation of the resulting metallatriene gives rise to bicyclic and linear polycyclic compounds 6 and 7, some of them bearing a polyquinane framework.

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…541, Scheme 35) with stabilized carbanions that contain pendant alkyne groups (e.g. 542, 547) resulted in a double annulation process [924]. The identity of the products was dependent on the length of tether separating the alkyne and carbanion units.…”