Stereoselective Control of the Cu Activation of ß,ß-Diboryl Acrylates for Allylic Coupling Protocols with Concomitant Lactonization.

The key to a successful C-B activation is to discriminate between two geminal boryl moieties that are exposed to the same reaction conditions. Here we describe a stereoselective C-B activation of ß,ß-diboryl acrylates forming exclusively the (Z)-α-borylalkenyl copper(I) key intermediate, for subsequent allylic alkylation reactions. The new borylated (Z)-skipped dienoates followed a feasible iodo-lactonization sequence for the preparation of borylated lactone cores, which can be used in drug discovery.

Site-Selective (Z)-α-Borylalkenyl Copper Systems for Nucleophilic Stereodefined Allylic Coupling.

1,1-Diborylalkenes can be transformed into (Z)-skipped dienes through CuI -phosphine catalyzed allylic coupling reactions. The energetically preferred formation of (Z)-α-borylalkenyl copper (I) species and the subsequent nucleophilic attack, explains the stereoselective nucleophilic substitution with allyl bromides. The eventual treatment of (Z)-skipped dienes with NaOt Bu promotes cyclization/aromatization patterns via enyne intermediates.