Formal Synthesis of Solanoeclepin A: Enantioselective Allene Diboration and Intramolecular [2+2] Photocycloaddition for the Construction of the Tricyclic Core

An enantioselective synthesis of an intermediate in the Tanino total synthesis of solanoeclepin A has been developed. The key step was an intramolecular [2+2] photocycloaddition, which led to the tricyclo[5.2.1.01, 6]decane core in six steps. The first photosubstrate, prepared through an indium‐mediated Barbier‐type reaction, gave an excellent [2+2] cycloaddition, but it could not be obtained in sufficient enantiopurity. The second photosubstrate, prepared through an asymmetric allene diborylation in high enantiomeric excess, gave the [2+2] cycloaddition product in high yield on irradiation at 365 nm on 20 g scale in a flow system. Other important steps were the replacement of a boronate group at the quaternary carbon by a vinyl group and diastereoselective cyclopropanation of an allylic alcohol. Short steps! An enantioselective diboration and intramolecular photocycloaddition are key processes in a six step synthesis of the tricyclo[5.2.1.01, 6]decane core of solanoeclepin A, which is the hatching agent of potato cyst nematodes. A Pd‐catalyzed diboration (91 % ee) and [2+2] photocycloaddition (in a flow system) were both carried out on a 20 g scale that provided the basis for a formal total synthesis of the natural product.