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(η5-C5H5)Co(CO)2 catalyses the [2 + 2 + 2] cycloaddition of silylated enediynes to furnish 1-trimethylsilyl and 1,11-bis(trimethylsilylated) A-ring aromatic steroids which unexpected hindered rotation of the trimethylsilyl groups.

Because of the extremely diverse physiological activity exhibited by the indole nucleus and its presence in a multitude of natural products selective alteration of its structure has commanded a considerable amount of synthetic attention. Part of this effort has involved the utilization of the 2,3-double bond in Diels-Alder and other cycloadditions. The authors report a novel mode of reactivity of this bond in the presence of eta-CpCo reagents: the (2 + 2 + 2) cycloaddition to two alkynes to provide the hitherto unknown 4a,9a-dihydro-9H-carbazole nucleus as incorporated in a variety of complex polycyclic dienes. This methodology demonstrates for the first time the feasibility of activating aromatic double bonds in CpCo-mediated cyclizations and provides a powerful means by which to fuse several rings onto the indole moiety in one step.

LBL-12662 Preprint

Evidence is presented for the reversible formation of metal-alkyne complex in the pyrolysis of eta/sup 5/-cyclopentadienyl-eta/sup 4/-cyclobutadiene-cobalt complexes. (DLC)

α,ω-Enynes are co-cyclised with alkynes and stoicheiometric amounts of dicarbonyl(cyclopentadienyl) cobalt to furnish bicyclic-diene cobalt complexes and their free ligands regiospecifically, the former being convertible into the latter by oxidative demetallation.

Polystyrene-supported eta/sup 5/-cyclopentadienylcobalt is catalytically active in the hydrogenation of carbon monoxide to give hydrocarbons. This activity must be due to a defined attached homogeneous cobalt species and not to deposited metal crystallites, and in contrast, soluble CpCo(CO)/sub 2/ is inactive and decomposed under hydrogenating conditions. The observed data characterize the title compound as the first catalyst activated to new activity on polymer attachment and the first immobilized homogeneous Fischer-Tropsch catalyst. 1 figure.

The synthesis of title cyclopentadienyl ligand I with C2 symmetry is described. I was designed to maximize the steric encumbrance of both diastereotopic faces, an effect achieved by annelation involving a stereospecifically 1,5-disubstituted bicyclo[2.2.2]octane frame. The system has been complexed to cobalt, titanium, and zirconium as model transition metals to demonstrate its effective function as a ligand in the formation of potentially catalytic organometallic complexes. As an example of this potential, the resulting titanocene dichloride was a catalyst precursor in the enantioselective hydrogenation of 2-phenyl-1-butene and 2-ethyl-1-hexene with unprecedented stereoselectivity.

The structure and properties of the title compd. (I) were compared to those of cyclopropabenzene and cyclobutabenzene. I reacted with (Me3P)2Ni[COD] to give Ni complex II.

Steroid compounds obtained by co-oligomerization of a side chain functionalized 1,5-hexadiyne with bis(trimethylsilyl)acetylene catalyzed by cyclopentadiene cobalt dicarbonyl, CpCO(CO)2, via intermediate benzocyclobutene formation followed by intramolecular cycloaddition to the sterospecific formation of the steroid nucleus. This constitutes a short steroid synthesis, five steps from commercially available acyclic precursor 1,5-hexadiyne and three steps from 2-methyl-cyclopent-2-enone.

3-Oxabicyclo[3,2,0]hepta-1,4-diene (3) has been synthesized by partial hydrogenation of 3-oxabicyclo-[3,2,0]hepta-1,4,6-triene (2).

The cobalt-mediated [2+2+2]cycloaddition of alkynes to heteroaromatic double bonds can be extended to the benzofuran nucleus, suggesting applications to the synthesis of morphinoids.

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 1545. DOI:10.1002/anie.198215450