Retro-Favorskii Reaction Employing Fluoride Sources

Abstract

In this study, we developed a novel and simple approach to perform retro-Favorskii type reactions comprising the use of a readily available fluoride source. Compared to the methods usually employed – which rely on the use of strong basic systems, such as KOH in toluene, at high temperatures and a reaction time of several hours – the one we propose employs milder conditions, shorter reaction times, is compatible with more solvents, and produces no appreciable amount of byproducts, thus allowing simple workup procedures. The reaction we describe is enabled by the strong basic character of the fluoride ion in absence of water. However, we observed that the reaction is remarkably tolerant to humidity and no anhydrous conditions are needed, making the reaction extremely straightforward to perform. The possibility of performing such reactions in a fast and reliable manner, without the appreciable formation of byproducts, can offer new interesting opportunities to efficiently employ propargyl alcohols derivatives as a masking group for carbonyls. The latter approach can be particularly interesting for the synthesis and derivatization of carbonyl-rich compounds – such as large, conjugated, electron-deficient systems or quinoid-based pigments – for which the limited solubility often precludes the synthesis of certain derivatives or their application in functional devices.

Preparation of different conjugated polymers characterized by complementary electronic properties from an identical precursor

“…Notably, we found that by employing n-butylammonium fluoride (TBAF) as a fluoride source, we could perform the desired reaction at a lower temperature (70 °C), for shorter times (<10 minutes) and with quantitative yields on model molecules. 54 As in the case of the reduction-rearomatization, also in this case, washing with water afforded high-purity products. 54 When the reaction was performed on the AH-P precursor, the colour changed to brown-red, and the fluorescence disappeared.…”

“…54 As in the case of the reduction-rearomatization, also in this case, washing with water afforded high-purity products. 54 When the reaction was performed on the AH-P precursor, the colour changed to brown-red, and the fluorescence disappeared. The resulting material was characterized as in the abovementioned case and identified as the desired AQ-P.…”

“…It is worth mentioning that since TBAF is compatible with many organic solvents, one has many options to find the best suitable conditions, including those for which the precursor does not dissolve (such as ketonic solvents and acetonitrile). 54 The latter aspect is particularly appealing to perform the transformation reaction directly on thin films of AH-P as AQ-P would otherwise be too insoluble to be processed. Similarly, thin films of AC-P can also be obtained directly from those of the precursor, since the latter does not dissolve in some of the solvents that one could employ for the necessary reductionrearomatization reaction, such as methanol or acetic acid in the specific case mentioned here.…”