Intermolecular catalytic Pauson-Khand reaction

Considerable effort has been devoted to achieving the intermolecular catalytic Pauson-Khand reaction. The mthenium complex-catalyzed reaction of an alkyne with an alkene such as ethylene or 2-norbornene under CO gave hydroquinone derivatives [79], with CO (2 mol) being introduced into the products (Eq. 11.36). This reaction is the first example of the preparation of hydroquinone derivatives by the reaction of alkynes and alkenes with CO, while hydroquinone is synthesized by the ruthenium-catalyzed reaction of 2 mol acetylene with 2 mol CO (Eq. 11.37) [80]. 

Pauson-Khand reaction. The intermolecular Pauson-Khand reaction of N- 2-alkenoyl)bomane-IO,2-sultams is totally stereoselective. The catalytic P-K reaction is promoted by small quantities of DME (or other hard bases including water). Reactions carried out in supercritical carbon dioxide are very efficient regardless of the substitution pattern of the alkyne unit. ... 

Enynes in which three or four atoms separate the double and triple bonds cyclize upon complexation to Co2(CO)g and subsequent heating to give bicyclic enones (equation 52). With the exception of slightly elevated temperatures the conditions required are no different than those of the stoichiometric procedure described earlier for reactive substrates in intermolecular Pauson-Khand reactions. The intramolecular cycloaddition cannot in general be carried out under catalytic conditions. Hex-l-en-5-yne, which would give a four-membered ring upon intramolecular cycloaddition, instead undergoes alkyne trimerization exclusively.3 The most extensively studied systems are those derived from hept-l-en-6-yne, as the products, bicyclo[3.3.0]oct-l-en-3-ones, are useful in the synthesis of numerous cyclopentane-based polycy-clics. 

The first report of a catalytic intermolecular cyclization was made by Pauson and Khand in 1974 [22], but the scope was limited to gaseous acetylene as the alkyne partner, strained olefins such as norbornene and norbornadiene as the alkene component, and TON s (turnover numbers) were modest (8-11). Several subsequent reports detailed the production of cyclopentenones from a substoi-chiometric amount of Co2(CO)g, but none were as efficient as Pauson s initial work [23,24]. Using ethylene as the alkene component, Rautenstrauch demonstrated the first efficient catalytic Pauson-Khand cyclization with a TON of 220, Eq. (5) [25]. A more general catalyst system employing (indenyl)Co(cod) was recently reported by Chung and Jeong, Eq. (6) [26]. The reaction was quite effec-... 

Pauson-Khand reaction. The sulfides have catalytic effects on both intramolecular and intermolecular version of the reaction. 

Terminal alkynes undergo oxidative coupling in the presence of the GuGl-TMEDA catalytic system in [G4GiIm]PF6 under aerobic conditions to produce 1,3-diynes. " Intermolecular Pauson-Khand reactions of strained alkenes with alkynes and Go2(GO)g were performed in [G4GiIm]PF6 either thermally or in the presence of... 

---