Palladium-Catalyzed Oligocyclizations of Some 2-Bromotetradec-1-ene-7,13-diynes Under Heck Reaction Conditions

Abstract

Synthesis of different substituted 2-bromotetradec-1-ene-7,13-diyne precursors can be easily achieved by using 1,7-octadiyne. The cyclization outcome of these precursors depends on the type of substituent at the terminal triple bond. Thus, when the terminal triple bond bears an electron-withdrawing group, such as a methoxycarbonyl group, a tetracyclic system with an annelated cyclopropane ring, will be formed. However, when the triple bond bears an electron releasing trialkylsilyl or phenyl group, the thermodynamically most stable aromatic compound, will be formed. When the terminal triple bond bears a proton (unsubstituted) or a group with an aptitude for migration, fulvene systems and tricyclic systems with an exo-double bond are being formed, respectively.The cyclization mechanism of these precursors can go via twofold Heck reactions followed by 5-exo-trig-carbopalladation (Heck-Heck-5-exo-trig-sequence). The variation in the outcome of these precursors excludes the other possibilities, such as intramolecular Diels-Alder, 6π-electrocyclization and 6-endo-trig-carbopalladation.The geminal substitution at the tether linking the vinyl bromide moiety would affect the yield of such precursors (2-bromotetradec-1-ene-7,13-diyne), but it has no effect on the outcome of the palladium-catalyzed transformations of these precursors.