Cobalt- versus ruthenium-catalyzed Alder-ene reaction for the synthesis of credneramide A and B.

The first synthesis of the natural products credneramide A and B was accomplished by utilizing Alder-ene reactions between a terminal alkene and an internal alkyne to generate the rather uncommon 1,4-diene substructure of these compounds. Moreover, two different short linear sequences toward these targets are evaluated using either a cobalt-catalyzed Alder-ene reaction of 1-chloropent-1-yne or a ruthenium-catalyzed Alder-ene reaction of 1-trimethylsilyl-1-pentyne with 5-hexenoic acid derivatives in the key step transformation. In addition, saponification of the primary Alder-ene product derived from the cobalt-catalyzed Alder-ene reaction led to credneric acid, the biological precursor of both natural products.