Advances in the Pauson-Khand Reaction: Development of Reactive Cobalt Complexes

Abstract

Three conceptually new methods employing reactive cobalt carbonyl complexes have been developed for the Pauson-Khand reaction. The first method involves activation of alkyne-dicobalt hexacarbonyls with "hard" Lewis bases. Primary amines dramatically promote the stoichiometric Pauson-Khand reaction. The active cobalt complexes produced in the system exhibit high reducing ability. The second method involves activation of dicobalt octacarbonyl with less electron-donating "hard" Lewis bases such as 1,2-dimethoxyethane and water. These Lewis bases were successfully utilized as a promoter for the catalytic Pauson-Khand reaction. The third method employs methylidynetricobalt nonacarbonyl cluster, which exhibits high reactivity in the catalytic Pauson-Khand reaction in the absence of activator. This may be due to facile coordination of the substrate to the metal center through dissociative and associative mechanisms and/or cleavage of one of the cobalt-cobalt bonds.

From D-galactose to enantiopure 3-azabicylclo[3.3.0]octen-7-one derivatives via Pauson-Khand reaction

“…1 The enantioselective version of this reaction using a chiral inductor covalently bonded to the alkene or the alkyne moiety had led in some cases to useful results. 2 By the use of carbohydrates as sources of chirality, these compounds have been considered as chiral substrates in the intramolecular PK reaction.…”

Rhodium catalyzed asymmetric Pauson-Khand reaction using SDP ligands

“…The results showed that SDP ligands were very effective in Rh-catalyzed Pauson-Khand reaction, and their complexes with rhodium could convert a variety of 1,6-enyne compounds into bicyclopentone derivatives under CO atmosphere in high yields with good enantioselectivities. The SbF 6 − was found to be a suitable counter anion of the catalyst, and 1,2-dichloroethane was the best choice of the solvent for Pauson-Khand reaction.Transition-metal-catalyzed Pauson-Khand reaction (PKR) [1][2][3][4] can conveniently convert an alkyne, an alkene and a carbon monoxide into cyclopentenone compounds in one step, which widely exist in natural products and bioactive molecules [5,6] . Owing to the wide application in organic synthesis, the Pauson-Khand reaction was extensively studied and a number of catalysts have been developed.…”

Cascade Reactions Involving Pauson–Khand and Related Processes

“…Carretero has reported several examples involving electrondeficient alkenes 3), such as α,β-unsaturated ketones, esters, nitriles, sulfoxides and sulfones. In these reactions they reach good yields of PK products (4) and isolate small amounts of dienes 5, that come from a β-elimination competitive reaction (Scheme 5) [26,27].…”

“…Complexation of propargyl aldehydes to cobalt also enhances the reactivity and enantioselectivity of the addition of alkylzinc reagents. This fact was used to create non-racemic enyne-ol 88 reacting the aldehyde 86 with bishomoallylzinc in the presence of a chiral bis-(sulfonamide) and Ti(O i Pr) 4 . The resulting complexed substrate 87 underwent the PKR promoted by TMANO in a one pot fashion (Scheme 25) [122].…”

“…Only a few of other reactions like the Diels-Alder, or the cyclotrimerization of alkynes can compete with the PKR, which consists formally of a [2 + 2 + 1] cycloaddition in which a triple bond, a double bond and carbon monoxide form a cyclopentenone [2][3][4][5][6][7][8][9][10][11][12]. This constitutes one of the best ways to construct cyclopentenones, which upon further transformations can be converted into structures present in numerous natural products (Scheme 1).…”