ChemInform Abstract: Straightforward Synthesis of 5‐Bromopenta‐2,4‐diynenitrile and Its Reactivity Towards Terminal Alkynes: A Direct Access to Diene and Benzofulvene Scaffolds.

Abstract

KERISIT, N.; TOUPET, L.; LARINI, P.; PERRIN, L.; GUILLEMIN, J.-C.; TROLEZ*, Y.; Chem. -Eur. J. 21 (2015) 16, 6042-6047, http://dx.

Synthesis and Reactivity of 5‐Bromopenta‐2,4‐diynenitrile (BrC5N): an Access to π‐Conjugated Scaffolds

“…In a similar fashion, we have recently demonstrated that the 5-bromopenta-2,4-diynenitrile (2; BrC 5 N), which bears one more C � C triple bond than BrC 3 N, reacted in an original fashion with triisopropylsilylacetylene in the above-mentioned conditions. [12] As with BrC 3 N, the unsymmetrical coupling product was not obtained. Instead, a conjugated dienynenitrile was isolated.…”

“…Moreover, we proved that the presence of halogenides (coming from BrC 5 N for instance) was mandatory for the success of the reaction, as reported before. [12] Thus, we deduced that the mechanism was a combination of two Sonogashira couplings and two halogenide additions [24] after the ynamine was formed. In a previous article, we showed that 1,6-addition on a similar structure (that is, MeÀ C � CÀ C � CÀ CN) was largely favored over 1,4-addition in THF.…”

“…The synthesis of BrC 5 N (2) has previously been described [12] following the brominative desilylation procedure of Kim and co-workers. [13] The synthesis of 5-[tri(propan-2-yl)silyl]penta-2,4-diynenitrile (3) has already been achieved from the reaction of (buta-1,3diyn-1-yl)tri(propan-2-yl)silane (triisopropylsilylbutadiyne; 4, which was formed in two steps from commercially available compounds), butyllithium, and tosyl cyanide.…”

“…Instead, a diene was obtained, involving the reaction of the amine and two equivalents of triisopropylsilylacetylene. [12] Therefore, we wanted to investigate the scope of this multi-component reaction by using different terminal alkynes and different secondary amines. In each case, CuI and [PdCl 2 (PPh 3 ) 2 ] were used as co-catalysts in THF at room temperature ( Table 2).…”

“…Therefore, the less efficient formation of the ynamine could explain finally the low formation of the corresponding diene. The first step being the formation of ynamine, [12] the fact that copper and palladium co-catalysts were necessary to the reaction let us think that Sonogashira couplings occurred. Moreover, we proved that the presence of halogenides (coming from BrC 5 N for instance) was mandatory for the success of the reaction, as reported before.…”