Ru(0)-Catalyzed Synthesis of Borylated-Conjugated Triene Building Blocks by Cross-Dimerization and Their Use in Cross-Coupling Reactions

Abstract

Abstract Borylated-conjugated polyenes are used widely as synthetic building blocks for the preparation of many biologically active molecules. Nevertheless, access to these building blocks has been limited. In this study, borylated-conjugated trienes were synthesized by Ru-catalyzed cross-dimerizations for use in cross-coupling reactions. A reaction of diphenylacetylene with (E)-butadien-1-ylboronic acid pinacol ester catalyzed by [Ru(naphthalene)(1,5-cod)] (10 mol %) at r.t., in benzene produced (1E,3E,5Z)-5,6-diphenylhexa-1,3,5-trien-1-yl boronic acid pinacol ester within 10 min in 93% yield. A similar treatment using pent-1-yn-1-yl boronic acid diisopropyl ester with methyl (E)-pentadienoate afforded methyl (2E,4E,6E)-7-(diisopropyloxyboraneyl)-6-propylhexa-2,4,6-trienoate in 89% yield. A series of mono- and diborylated-conjugated trienes were synthesized by cross-dimerization and assessed for their potential use in cross-coupling reactions. Using this protocol, the total synthesis of navenone B, a sea slug pheromone, was achieved in only three steps in 45% total yield.