The Intermolecular Pauson–Khand Reaction

Abstract

Five membered carbocycles are important building blocks for many biologically active molecules. Moreover, substituted cyclopentenones (e.g. cyclopentenone prostaglandins) exhibit characteristic biological activity. The efficiency and atom economy of the Pauson-Khand reaction render this process potentially one of the most attractive methods for the synthesis of such compounds. Although it was discovered in its intermolecular form, the scope of the intermolecular Pauson-Khand reaction has always been limited by the poor reactivity and selectivity of the alkene component. The past decade, especially the last three years, has seen concerted efforts to broaden the scope of this reaction. In this overview, we provide a comprehensive and critical coverage of the intermolecular Pauson-Khand reaction based on the reactivity characteristics of different classes of alkenes and a rationalization of successes and misfortunes in this area.

(Di‐tert‐butylphosphanylethyl)cyclopentadienylnickel Chelates with Alkyl, Alkenyl, Aryl, and Alkynyl Ligands: Hints to Cumulenylidene Resonance Forms

“…(Alkyne)hexacarbonyldicobalt complexes can easily be prepared by treatment of the alkyne with dicobalt octacarbonyl. Such complexes are important in the context of the Pauson–Khand reaction, in which coupling of the alkyne with an alkene results, after CO insertion, in valuable cyclopentenones . Manning et al reported the syntheses of some nonchelate cyclopentadienyl triphenylphosphane alkynyl nickel complexes and performed reactions with dicobaltoctacarbonyl resulting in the formation of trimetallic alkyne hexacarbonyldicobalt complexes with a nickel substituent at the coordinated triple bond , .…”

“…Such complexes are important in the context of the Pauson-Khand reaction, in which coupling of the alkyne with an alkene results, after CO insertion, in valuable cyclopentenones. [58][59][60][61][62][63][64][65] Manning et al reported the syntheses of some nonchelate cyclopentadienyl triphenylphosphane alkynyl nickel complexes and performed reactions with dicobaltoctacarbonyl resulting in the formation of trimetallic alkyne hexacarbonyldicobalt complexes with a nickel substituent at the coordinated triple bond. [66,67] They mentioned that the parent compound with the unsubstituted alkynyl ligand coordinated to Co 2 (CO) 6 rapidly decomposed, so that only an IR spectrum could be Scheme 5. measured for characterization.…”

Characteristic reactions of group 9 transition metal compounds in organic synthesis

“…The hydroformylation reactions [200 -216] are used for preparing aliphatic aldehydes whose number of carbon atoms is increased by one, as shown in eqn (32).…”

Metallacycle-mediated cross-coupling in natural product synthesis

“…To date, the vast majority of these applications have been conducted in intra - rather than inter molecular settings. 136 That said, there have been notable examples of the use of intermolecular Pauson-Khand reactions in natural product synthesis. These processes are, as illustrated in the bottom portion of Figure 36, quite complex.…”