Pauson−Khand Reaction Induced by Molecular Sieves

Abstract

The Pauson−Khand reaction still has a relatively low scope with respect to the used carbon skeleton, while yields are low in many other cases. We have observed that the addition of molecular sieves improves yields remarkably. Experimental protocol is extremely easy, and it has been applied to several substrates including the less favorable ones.

The use of silicon-based tethers for the Pauson-Khand reaction

“…Using each of the compounds 1–4 , we first tested five alternative promoters to NMO. These were cyclohexylamine[16]; 1,4-dioxane/2M ammonium hydroxide[17]; trimethylamine N -oxide, 4 molecular sieves[18]; n -butylmethylsulfide[19] and microwave irradiation[20]. As previously, the dicobalt octacarbonyl complexes of each compound were first prepared and characterised, prior to addition of the promoter.…”

Allylsilyl Propargyl Ethers as Substrates for Intramolecular Pauson–Khand Reactions

“…Attempts to promote the cyclization by the use of molecular sieves [11] (entry 8) or NMO [12] (entry 9) did not lead to any improvement in the cyclization yield. However, the use of n-butyl methyl sulfide as a promoter [3b] in 1,2-dichloroethane as solvent afforded the bicycles 9a and 9b in yields of 72% and 70% respectively, and these conditions were adopted for subsequent studies.…”

Cascade Reactions Involving Pauson—Khand and Related Processes

“…We have shown the positive effect of molecular sieves in both the catalytic and the stoichiometric version of the reaction. These zeolites probably retain CO molecules, increasing conversions even with non favorable substrates, such as substituted olefins [61,62].…”