Cobalt-mediated synthesis of tricyclic dienes incorporating fused four-membered rings. Unprecedented rearrangements and structural characterization of a cobalt-diene complex by two-dimensional NMR spectroscopy

Metal-Assisted Cycloaddition Reactions in Organotransition Metal Chemistry

“…[822][823][824][825] Besides with cobalt, 826 such reactions of two alkynes and an alkene, giving free cyclohexadienes, are also known to be catalyzed by complexes of iron, 827 nickel, 828 rhodium, 829 and palladium. 830 832 intramolecular with several stereoisomeric endiynes, 833 (e.g., eq 135), and intermolecular with two equivalents of alkyne (diphenylacetylene, dimethyl acetylenedicarboxylate) and 1 equiv of alkene (dicyclopentadiene, norbornene) (Scheme 75).…”

Catalytic Version of Enediyne Cobalt‐Mediated Cycloaddition and Selective Access to Unusual Bicyclic Trienes

“…[11] The next stage of our study was to determine if we could avoid using a stoichiometric amount of cobalt in the more challenging cycloaddition of yne-yne-enes. [12] We initially selected the yne-yne-ene 3 a bearing a tether involving a Thorpe-Ingold effect, an ester moiety to stabilize the desired 1,3-cyclohexadiene, [13] and a nonsubstituted double bond to prevent any unfavorable steric effect. To our delight, in the presence of 5 mol % of [Co(H)A C H T U N G T R E N N U N G (PMe 3 ) 4 ] we obtained the first catalytic cobalt-catalyzed cycloaddition of enediynes at room temperature without external activation to generate the desired 1,3-cyclohexadiene 4 a, which was isolated in good yield ( Table 2, entry 1).…”

Enantiomerically Pure Vinylcyclopropylboronic Esters

“…[14] The olefination of aldehyde 8 was achieved by a conventional Wittig reaction (90 %) or a Peterson reaction (85 %). [15] Both sequences were performed numerous times and proved to be equally reliable for providing vinylcyclopropane 9 in high yield (Scheme 1). Scheme 1.…”