The absolute control of the regiochemistry of a cobalt-catalyzed 1,4-hydrovinylation reaction is achieved by alternation of the ligands applied. While the dppe/dppp ligands led to the formation of the branched product, the herein described application of the SchmalzPhos ligand generates the corresponding linear product in both excellent yields and regioselectivities. The catalyst system exhibits a high tolerance toward functional groups, and the very mild reaction conditions allow the synthesis of 1,4-dienes without isomerization into conjugated systems.

No abstract

The cobalt-catalysed Glaser-type coupling of terminal alkynes was achieved utilising nitrobenzene as a stoichiometric oxidising agent under reductive conditions. The proposed electron transfer from zinc powder to a nitrobenzene coordinated to the cobalt centre initiates the coupling of the coordinated alkynes. Other aryl-, alkenyl-, alkyl-, and silylacetylenes besides phenylacetylene could also be coupled to generate the 1,3-diynes in moderate to very good yields.

The cobalt(I)-catalyzed 1,4-hydrovinylation reaction of allyl trimethylsilane and allyl pinacol boronic ester with symmetrical and unsymmetrical 1,3-dienes generates building blocks for the in situ allylboration or the Lewis acid induced allylation reaction utilizing the corresponding allyl silane derivatives. The products of these three-component reactions are hydroxy-functionalized 1,4-dienes which can be used for the synthesis of pyranones. An alternate reaction sequence for the synthesis of the hydroxy-functionalized 1,4-dienes by performing the allylation first followed by the cobalt-catalyzed 1,4-hydrovinylation is also possible. Accordingly, polyfunctionalized complex structures can be generated by both approaches in a convergent fashion.