The Tandem Pauson‐Khand Reaction

Abstract

The conditions for the novel tandem Pauson‐Khand reaction have been explored. The highly functionalized tetracyclic compounds 11c, 11d, and 16 were prepared from the ene‐diynes 4c, 4d, and 10 by treatment with 2 equiv. of [Co2(CO)8] and 4‐methylmorpholine N‐oxide (NMO) or Me3NO in yields of 24, 22, and 53%, respectively (Table). In the presence of 1–3 equiv. of H2O added to the NMO used for induction of the Pauson‐Khand reaction of 6d, a mixture of cyclopentanones 17/18 and cyclopentenones 12/13 was obtained (Scheme 5). The first example of a [Co2(CO)6]‐induced highly stereoselective ene reaction is described. To account for these results, the formation of intermediates are proposed (Schemes 6 and 7) which hitherto have not been considered in the mechanistic description of the Pauson‐Khand reaction.

Synthesis and reactions of two stereoisomeric [4.5.5.5]fenestranes with bridgehead substituents

“…8 This cyclocarbonylation reaction gave the expected stereoisomeric bicyclo [3.3.0]enones 8 and 9 in yields of 89% and 79%, respectively. In addition the saturated byproducts 10 and 11 were isolated in a total yield of 20% with the trans-isomer 11 being obtained pure (Scheme 2).…”

Cascade Reactions Involving Pauson—Khand and Related Processes

“…It was clear from the fact that compound 140 failed to react, that the second PKR had to start from an intermediate metallacycle rather than from the uncomplexed final cyclopentenone. Thus, cobalt complex 137 would lead to 138 were both metal clusters would interact giving intermediate 139 which would evolve in the usual way to the final product (Scheme 42) [149]. These systems have been obtained later by Chung's group using cobalt nanoparticles as commented above (Sect.…”

Topospecific Reactions of a [5.5.5.5]Fenestradiene with [Fe2(CO)9]

“…elimination in an isolated yield of 46%. This lack of sigmatropic rearrangement in the case of 2a and 2b is in contrast to the successful Claisen-type [3,3]sigmatropic rearrangements at the a-as well as at the b-face of [4.5.5.5]fenestranes [ll]. To the best of our knowledge, this mode of reaction of allylic alcohols with an N,N-dimethylformamide diacetal has not been described4).…”