Beschleunigung der Pauson‐Khand‐Reaktion durch primäre Amine

Abstract

Ökonomisch und praktisch sind neu entwickelte Reaktionsbedingungen für die Pauson‐Khand‐Reaktion, die den Befund nutzen, daß primäre Amine diese Reaktion beschleunigen. Im einen Fall werden mehr als drei Äquivalente Cyclohexylamin in 1,2‐Dichlorethan bei 83 °C verwendet und im anderen ein Gemisch aus 1,4‐Dioxan und 2 M wäßrigem NH3 (1/3, v/v) bei 100°C, Unter diesen Bedingungen ist z.B. die unten gezeigte Cyclisierung nach 5 bzw. 15 min vollständig abgelaufen, und das Produkt kann in 99 bzw. 93% Ausbeute isoliert werden.

Vinyl Sulfoxides as Stereochemical Controllers in Intermolecular Pauson–Khand Reactions: Applications to the Enantioselective Synthesis of Natural Cyclopentanoids

“…However, regardless of the substrate (1 a or 1 i) and solvent used (toluene or acetonitrile at 80 8C), we obtained a complex mixture of products in which neither the PK cyclopentenone nor the 1,3-diene could be detected. A similar result was also observed when the reaction was carried out in the presence of cyclohexylamine as the promoter [5] in toluene at 90 8C. As these disappointing results could be due, at least partially, to the low thermal stability of the sulfinyl group, we turned to PK reactions promoted by amine N-oxides, which usually involve the use of very mild reaction conditions (usually 0 8C or room temperature).…”

“…[2] Since the first PK reactions were described in the early 1970s as involving heating stoichiometric amounts of dicobaltoctacarbonyl, alkyne, and alkene, [3] huge progress has been made. Among the key advances in this reaction, those worthy of notice are the discovery of efficient promoters that allow the process to be performed under mild conditions (for instance, tertiary amine N-oxides, [4] secondary amines, [5] thioethers, [6] silica gel, [7] and molecular sieves [8] ), the development of catalytic cobalt procedures, [9] the extension of the reaction to other metal mediators, such as rhodium, [10] ruthenium, [11] titanium [12] and iridium, [13] the application of the reaction to the synthesis of complex natural products, [2,14] the deep theoretical study of the mechanistic aspects of the reaction, [15] and the development of highly efficient diastereoselective and asymmetric versions of PK reactions. [16] Despite this impressive progress, however, some important limitations still remain.…”

A “Catch‐and‐Release” Protocol for Alkyne‐Tagged Molecules Based on a Resin‐Bound Cobalt Complex for Peptide Enrichment in Aqueous Media

“…In the absence of TFA, complex 4 appeared to be stable under neutral aqueous conditions. Other additives, such as tetrabutylammonium fluoride,21 ethylenediamine,22 2‐aminoethanol22 and cyclohexylamine,23 which are known to decomplex alkyne–cobalt complexes in organic solvents, showed diminished decomplexation ability with complex 4 in water. When free alkyne 1 was treated with TFA, no reaction was observed, which indicates that amine 2 was indeed obtained by the Nicholas reaction from complex 4 .…”

Pauson‐Khand‐Reaktion: Beginn der katalytischen Ära

“…Aufbauend auf ihren eigenen Arbeiten zur stöchiometrischen PKR13 verwendeten Sugihara et al harte Lewis‐Basen als Additive in der inter‐ und intramolekularen CPKR mit 0.01–0.03 Äquivalenten Octacarbonyldicobalt( 0 ) 14. Harte Lewis‐Basen schwächen die Ligandenbindung niedervalenter organischer Übergangsmetallkomplexe.…”

“…Unter Sugihara‐Bedingungen konnte die katalytische Reaktion nicht in DME als Lösungsmittel ausgeführt werden 15. Cyclohexylamin erwies sich zwar als der beste Promotor in der stöchiometrischen Variante,13 war in der CPKR aber bis zu einem CO‐Druck von 7 atm wirkungslos 14. Dagegen verwendeten Krafft et al Cyclohexylamin als Additiv in einer thermischen CPKR (Tabelle 1, Nr.…”