16-01

R.A. Kleinnijenhuis, B.J.J. Timmer, G. Lutteke, J.M.M. Smits, R. de Gelder, J.H. van Maarseveen, H. Hiemstra,

Formal synthesis of solanoeclepin A: enantioselective allene diboration and intramolecular [2+2] photocycloaddition for the construction of the tricyclic core,

Chem. Eur. J. 22 (2016) 1266-1269

Abstract

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[5.2.1.0^1, 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.