Reactivity of Functionalized Ynamides with Tetracyanoethylene: Scope, Limitations and Optoelectronic Properties of the Adducts

Abstract

The reactivity of functionalized ynamides and arylynamines with tetracyanoethylene at room temperature was evaluated. In most cases, the corresponding 1,1,4,4-tetracyanobutadienes (TCBDs) were obtained in good to excellent yields through a [2+2]-cycloaddition/[2+2]-retro-electrocyclization sequence. The influence of diverse functional groups on the yield of the reaction was investigated, in particular concerning multiple ynamides. These TCBDs were characterized by various spectroscopic techniques and electrochemistry and X-ray diffraction in some cases.

Helicenes Grafted with 1,1,4,4‐Tetracyanobutadiene Moieties: π‐Helical Push–Pull Systems with Strong Electronic Circular Dichroism and Two‐Photon Absorption

“…Compound 3 a was then subjected to Hsung conditions to form ynamide 4 a in a modest 26 % yield (unoptimized due to the very low solubility of 3 a ). Reaction of 4 a with TCNE through [2+2] cycloaddition followed by retro‐electrocyclization, (CA‐RE sequence) finally afforded the target carbo[4]helicene‐TCBD derivative 1 a in 99 % yield. The product was fully characterized; its 1 H NMR spectrum featured the typical signals for the [4]helicenic core (see the Supporting Information), such as two typical downfield signals of the shielded H 11 and H 12 (see Figure ) at δ =9.33 and 8.96 ppm, respectively; its 13 C NMR spectrum showed the characteristic peaks of the four cyano groups resonating between δ =110 and 113 ppm, unambiguously indicating the presence of the TCBD moiety.…”

“…The identity of these donors varies, and the yield of the reaction strongly depends on their nature. Some years ago, some of us reported the synthesis of TCBDs from ynamides, which served as electron‐rich alkynes ,. Their reduction potentials were among the lowest hitherto reported for TCBDs, allowing us to envisage promising applications by tuning the properties of extended π‐systems.…”

The [2+2] Cycloaddition‐Retroelectrocyclization (CA‐RE) Click Reaction: Facile Access to Molecular and Polymeric Push‐Pull Chromophores

“…[29,30] Recently,a ctivation by donors featuring nitrogen atoms directly attached to the alkyne was found to be quite effective. [32] Apart from the purely organic systems,arepresentative organometallic substance,f errocene,h as often been employed as ad onor substituent. [31] They ields of the triazene derivatives were good, whereas the alkynes activated by ynamide units afforded the TCBDs nearly quantitatively (92-98 %; Table 1, entry 16).…”

“…[31] They ields of the triazene derivatives were good, whereas the alkynes activated by ynamide units afforded the TCBDs nearly quantitatively (92-98 %; Table 1, entry 16). [32] Apart from the purely organic systems,arepresentative organometallic substance,f errocene,h as often been employed as ad onor substituent. Mochida et al optimized the conditions and reported aC A-RE reaction of ethynylferrocene with TCNE in yields up to 99 % ( Table 1, entry 17).…”

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

“…The same kind of results was observed when reacting compound 11d with TCNE. It confirms that Nalkylynamines, contrary to N-arylynamines, [22,23] are not able to afford TCBDs by reaction with TCNE in these conditions.…”