(Indenyl)cobalt(I)-Catalyzed Cocyclization of Alkyne, Alkene, and Carbon Monoxide to Cyclopentenones

Abstract

The development of simple and general methods for the preparation of cyclopentenones from readily available substrates is one of the major challenges of metal-promoted organic synthesis.2 One of the most effective methods of synthesis of cyclopentenones is the Pauson-Khand reaction (PKR).s-S However, most PKRs are stoichiometric reactions. There have been many attempts6 to catalyze the PKR, but the only truly catalytic reactions described so far are very limited.7.8 A number of alternatives to the PKR have been reported that involve various transition metals as catalysts or promoters.2 Herein we report the development of a new catalyst system that proceeds under mild reaction conditions to give cyclopentenones in excellent yields.Our new process has been successfully achieved by introducing 1,5-cyclooctadiene(indenyl)cobalt(I) complex ( l ) 9 as a catalyst. Complex 1 is moderately stable and can be stored for a long time

Metal-Assisted Cycloaddition Reactions in Organotransition Metal Chemistry

“…Only more recently turnover numbers of several hundred have been achieved with modified cobalt catalysts under CO pressure. [781][782][783] The reaction is very regioselective with respect to the acetylene, and the CO group is normally found next to the bulkier R group of the alkyne (R 1 in eq 125), i.e., with terminal acetylenes, the substituted terminal is exclusively found at the C-2 position of the cyclopentenone. 756,775 This infers that the olefin coordinates to cobalt from the less hindered side of complex 480.…”

Cationic cobalt(I) catalysts for the asymmetric cyclocarbonylation of 1,6-enynes

“…Characterization of the cyclocarbonylation product 3 was in agreement with data published by others. 12 A dry 50-ml Schlenk tube was equipped with a magnetic stirrer bar and a flexible Teflon tube connected to a 60-ml stainless steel autoclave (Medimex, Lenzburg, Switzerland) by a septum. The complex (0.03 mmol) was added to the Schlenk tube and stirred in 12 ml of DME under a CO atmosphere for 15 min at room temperature.…”

The Pauson–Khand Reaction: the Catalytic Age Is Here!

“…Problems associated with the very labile [Co 2 (CO) 8 [18] Under high pressures of CO, very good conversions were obtained for both intramolecular cyclizations and intermolecular reactions between constrained alkenes and terminal alkynes (Scheme 5); TONs up to 97 in 40 h). Experiments with nonconstrained alkenes, however, were unsuccessful.…”

“…[4,5] At that time, catalytic systems that could induce asymmetry were only speculative, presumably because in most of the cases they required very harsh conditions (high temperatures and very high pressures of carbon monoxide). [6,10,18,20] In 1996, however, Buchwald and Hicks reported the first example of an asymmetric PKR involving a catalytic amount of a chiral titanocene complex (Scheme 12). [52] Following their own work on the use of the highly active species [Cp 2 Ti(CO) 2 ] as a catalyst for the cyclization of enynes under mild conditions, they succeeded in inducing asymmetry by employing the enantiomerically pure analogue (S,S)-[(ebthi)Ti(CO) 2 ] (8)-generated in situ from (S,S)-[(ebthi)Ti(Me) 2 ] (Scheme 13, ebthi = ethylene-1,2-bis(h 5 -4,5,6,7-tetrahydro-1-indenyl)).…”

“…7-2 medium 2 12 [28] [Co 4 (CO) 11 P(OPh) 3 ] [c] 5 7-2 -1 13 [20] [Co(acac) 2 ] + NaBH 4 30-40 100-7 low 0 14 [18] indenyl cobalt(i) 15 97-10 -0 15 [27] [Co 4 (CO) 12 ] 10 50-38 medium 2 16 [45,46] …”