Synthesis of Boronates with a Protoilludane Skeleton

In memory of David A. Evans

Abstract

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 photochemical 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.

Key words

borylation - domino reactions - hydroboration - natural products - photochemistry - stereoselective synthesis

Publication History

Received: 06 February 2023

Accepted after revision: 14 March 2023

Article published online:
17 April 2023

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