A 14-step approach to enantiopure cochlearol B is reported. This renoprotective meroterpenoid was isolated from the extracts of <i>Ganoderma cochlear</i> in 2014. This molecule features a unique core structure containing a densely substituted cyclobutane ring with three stereocenters. Our strategy employed an organocatalytic Kabbe condensation en route to the key chromenyl triflate. A subsequent Catellani reaction incorporated the remaining carbon atoms featured in the skeleton of cochlearol B. An ensuing visible-light-mediated [2+2]-photocycloaddition closed the cyclobutane ring and formed the central bicyclo[3.2.0]heptane core. Notably, careful design and tuning of the Catellani and photocycloaddition reactions proved crucial in overcoming undesired reactivity, including cyclopropanation reactions and [4+2]-cycloadditions.

Total synthesis of cochlearol B via visible light-enabled [2+2]-cycloaddition approach

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ACS Fall 2022

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