Rhodium Complex-Catalyzed Pauson−Khand-Type Reaction with Aldehydes as a CO Source

Abstract

With aldehydes as a CO source under solvent-free conditions, rhodium complex efficiently catalyzed an intramolecular carbonylative alkene-alkyne coupling (Pauson-Khand-type reaction) and various bicyclic enones were obtained in high yield. Experiments under argon flow and a 13C-labeling experiment suggested that almost no free carbon monoxide was generated in this reaction. When noncationic rhodium complex with chiral phosphine was used as a chiral catalyst, the reaction proceeded enantioselectively to give various chiral cyclopentenones in up to 90% ee under solvent-free conditions.

Rhodium‐Catalyzed Asymmetric Aqueous Pauson–Khand‐Type Reaction

“…Cinnamylaldehyde gave the best results in both optical and chemical yields (Table 1, entry 4). Electron-donating p-methoxybenzaldehyde gave a complicated reaction mixture with poor product yield, while electron-deficient p-chlorobenzaldehyde furnished the desired product in both good yield and enantioselectivity (Table 1, entries 11,12). It is particularly noteworthy that we found the electronic properties of the aromatic aldehydes were responsible for both the enantioselectivity and yield of the corresponding substituted-cyclopentenone products (Table 1, entries 10-12).…”

“…Recently, two independent groups led by Morimoto/Kakiuchi and Shibata reported notable accomplishments in the investigation of aldehydes as CO surrogates. [11,12] These findings enable us to use a nontoxic "carbon monoxide" like reagent for carbonylation reactions.…”

Selective enhancement effects of silver salts on the transition metal-catalyzed synthesis of gem-difluorinated heterocyclics using 2,2-difluorohomopropargyl amides

“…Other silver salts did not have this effect (entries 10-13, Table 3) [13]. The choice of solvent and concentration was also important to prevent the formation of by-products (mainly the dimer of 8).…”

Cascade Reactions Involving Pauson–Khand and Related Processes

“…The enantiomeric excess reached when using a chiral ligand is higher with this methodology than when using CO atmosphere in the absence of the aldehyde (Scheme 39) [144,145].…”

“…Their first studies used suitable diendiynes 141-143 that gave the corresponding tetracyclic biscyclopentenones. These were described as precursors of dicyclopenta[a, d] (144) and [a, e]pentalenes (145). The same methodology allowed the synthesis of [5.6.6.5] systems (146) where the central decaline system was cis fused (Scheme 43) [150][151][152].…”