Synthesis of Boronates with a Protoilludane Skeleton

Naturally occurring sesquiterpenes with a protoilludane skeleton are frequently oxygenated at carbon atoms C4 and C8. Boronic acid pinacol esters (BPin) are potential precursors for hydroxy groups at these positions and synthetic methods have now been developed for their preparation. Introduction of a boronate in position C4 was achieved by Cu-catalyzed hydroboration of a photochemically generated cyclobutene precursor, which displayed the complete C15-carbon skeleton of protoilludanes. Introduction of BPin at carbon atom C8 was possible by starting with an alkenyl boronate as precursor in a photo-chemical transformation. A two-photon reaction cascade allowed for creation of the complete protoilludane skeleton with BPin selectively positioned at C8. Subsequent reactions were studied and the oxidative transformation of the boronates into the respective alcohols was shown.

Automated summary

Naturally occurring sesquiterpenes with a protoilludane skeleton are frequently oxygenated at carbon atoms C4 and C8. Boronic acid pinacol esters (BPin) can serve as precursors for hydroxy groups at these positions and synthetic methods have been developed for their preparation. Introduction of a boronate at position C4 was achieved through Cu-catalyzed hydroboration of a photochemically generated cyclobutene precursor, while introduction of BPin at carbon atom C8 was accomplished through a photochemical transformation starting with an alkenyl boronate. Subsequent reactions showed the oxidative transformation of boronates into the respective alcohols.