Phosphane Sulfide/Octacarbonyldicobalt-Catalyzed Pauson - Khand Reaction Under an Atmospheric Pressure of Carbon Monoxide

Abstract

Convenient access to cyclopentenones is provided by catalytic intra- and intermolecular Pauson - Khand reactions in the presence of octacarbonyldicobalt and tributylphosphane sulfide (see scheme). In contrast to other reactions of this type, they proceed under mild conditions (70 degrees C, 1 atm CO), and commercially available [Co(2)(CO)(8)] can be used without further purification.

New promoters for the molybdenum hexacarbonyl- mediated Pauson–Khand reaction

“…Surprisingly, the inorganic salts like Na 2 SO 4 also showed some activity, although the reaction was slow and very dirty ( Table 1, Entry 57). Several additives that were shown to have positive effects in cobalt-mediated PKR (hard Lewis bases such as NMO and dioxane, Ph 3 PS 25 or triethylamine) failed to give molybdenumpromoted PKR. Pyridine and 2,6-dimethylpyridine show some beneficial effect, but were not sufficiently attractive for further studies -considering their toxicity, also (Table 1 Entries 15, 16).…”

Catalytic Pauson–Khand reaction in ionic liquids

“…Co 2 (CO) 8 (stabilised with 1-5% hexane) was purchased from Strem Chemicals and used without further purification. The solvents were purified according to literature procedures [38].…”

“…For reactions carried out at higher CO pressures, analogous quantities of Co 2 (CO) 8 , substrate, and ionic liquid were added to a glass inlet which was transferred to a stainless steel autoclave under nitrogen stream; the autoclave was quickly purged with CO, pressurised with CO, heated to the desired temperature and the reaction mixture vigorously stirred. Upon reaction completion the organic products were extracted as previously specified and the yield assigned either by GLC (internal standard method, n-dodecane) or by flash-chromatography purification.…”

“…A first milestone in this perspective has been posed by the discovery that the annelation, which in its first applications required stoichiometric amounts of dicobalt octacarbonyl, could be carried out under catalytic conditions [5]. Since then, a number of promoters (hard [6] and soft donors [7][8][9][10]) has been successfully employed aiming at carrying out the reaction under ambient conditions. Among the recent developments in this field we acknowledge the binding of the catalyst onto organic [11] or inorganic matrices [12,13] and the replacement of carbon monoxide by suitable aldehydes [14,15].…”

“…In this framework, we deemed it worthwhile to consider the catalytic PKR for its synthetic relevance. In the course of our investigation, the stoichiometric use of Co 2 (CO) 8 for the intermolecular thermal or amine oxide promoted PKR in the IL 1-butyl-2,3-dimethylimidazolium hexafluorophosphate ([bmim]PF 6 ) was reported [34]. Here, we describe the results of our studies on imidazolium-based ionic liquids as media for the Co 2 (CO) 8 catalysed PKR focusing our attention mainly on bifunctional enynes as substrates (Scheme 1).…”