1,6-Dibromohexa-1,3,5-triene − Stereocontrolled Synthesis of Monosubstituted and Disubstituted Hexatrienes by Palladium-Catalysed Cross-Coupling Reactions

Abstract

1,6‐Dibromohexa‐1,3,5‐triene, previously described by us and easily obtained from 5‐bromopenta‐2,4‐dienal by condensation with bromomethylene triphenylphosphorane, is a versatile precursor for the synthesis of conjugated 1,3,5‐trienic derivatives of controlled configuration. In this paper, we describe the stereocontrolled synthesis of E,E,Z, E,E,E and Z,E,Z isomers of α‐bromo‐ω‐substituted‐1,3,5‐hexatrienes and 1,6‐disubstituted‐1,3,5‐hexatrienes. The synthesis is based on palladium‐catalysed single or double cross‐coupling reactions between the three isomers − 1E,3E,5Z, 1E,3E,5E and 1Z,3E,5Z − of the intermediate 1,6‐dibromohexa‐1,3,5‐triene and various organozinc reagents.

Metalated Heterocycles and Their Applications in Synthetic Organic Chemistry

“…Furylzincs have also been used in different Negishi coupling reactions, for example, to aryl halides, β-iodo-β,γ-enones, tosyloxymethylenefuranones, or dibromotrienes 778 such as compound 557 , which reacts with 2-furylzinc bromide ( 558 ) under palladium(0) catalysis to give the triene 559 (Scheme ),778b a reaction which has also been carried out with 2-thienylzinc bromide 778b 152 …”

Practical and Convenient Synthesis of 1,6-Di- or 1,2,5,6-Tetra-arylhexa-1,3,5-trienes by the Dimerization of Pd(0)-Complexed Alkenylcarbenes Generated from π-Allylpalladium Intermediates

“…1,6-Diarylhexa-1,3,5-trienes serve as fluorescent probes in biological studies, and 1,3,4,6-tetraarylhexa-1,3,5-trienes have a structure consisting of organic fluorophores, which exhibit aggregation-induced emission enhancement . Although several synthetic approaches to 1,6-diarylhexa-1,3,5-trienes have been developed, substrate scope is narrow, and some methods require elaborate substrates. − Thus, more general protocols for the synthesis of 1,6-diarylhexa-1,3,5-trienes are still of high interest. Among their reported methods, the dimerization of the Pd(0)-complexed 3-aryl propenylcarbene appears to be an ideal approach due to its high functional group tolerance.…”

Effective and Highly Stereoselective Coupling with Vinyldiazomethanes To Form Symmetrical Trienes

“…After removal of the solvent under reduced pressure, the residue was purified by column chromatography (hexanes:ethyl acetate = 100:1) to give the product triene. Products were identified by comparison to the spectral properties of the known compounds. − The ( E,Z,E )-isomer has also been reported 7b. Pyrazoles were identified by their characteristic NMR, IR, and mass spectral data.…”

“…Furthermore, vinyldiazoacetates exhibit high diastereocontrol in cyclopropanation reactions, but the stereoselectivity from vinyldiazomethanes is unknown. Symmetrical trienes have been previously prepared by Wittig reactions, palladium-catalyzed coupling reactions, and by other methods . We now report a highly efficient method for the synthesis of symmetrical trienes from cinnamaldehydes, the highly stereoselective trapping of vinyl carbene intermediates with styrene, and mechanistic considerations related to the method for formation of vinyldiazo compounds.…”