Synthesis of cyclopentenones: The new catalytic cocyclization reaction of alkyne, alkene, and carbon monoxide employing catalytic Co(acac)2 and NaBH4

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

“…[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)).…”

“…Inspired by work of Lautens and co-workers, [19] Lee and Chung reported that a catalytic combination of [Co(acac) 2 ] and NaBH 4 can effectively promote both inter-and intramolecular versions of the PKR under high pressures of CO. [20] Despite the fact that the use of a strong reducing agent may limit the range of compatible functional groups, this system gave high TONs. It was presumed by the author that NaBH 4 prevented the formation of inactive cobalt species.…”

“…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] …”

The Pauson-Khand-Type Reaction Catalyzed by Transition Metal Nanoparticles

“…They can be good candidates as supports. Thus, cobalt metal was deposited on mesoporous materials including MCM-41 and SBA-15 by reduction of cobalt halide or decomposition of Co 2 (CO) 8 in the presence of mesoporous materials. Cobalt loading was adjusted to 9-10 wt%.…”

“…After promoters were found, many research groups tried to find cobalt compounds, which easily provided an empty coordination site and was easily generated in solution. Actually, many useful catalytic systems such as (indenyl)Co(CO) 2 , (indenyl)Co(cod), Co 2 (CO) 8 , and Co 4 (CO) 12 were developed. 7 From the study on homogeneous catalytic systems, any system capable of generating in situ cobalt carbonyl species in a solution could be used as a catalyst.…”