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The electrophilic activation of various substrates via double or even triple protonation in superacidic media enables reactions with extremely weak nucleophiles. Despite the significant progress in this area, the utility of organophosphorus compounds as superelectrophiles still remains limited. Additionally, the most common superacids require a special care due to their high toxicity, exceptional corrosiveness and moisture sensitivity. Herein, we report the first successful application of the "Brønsted acid assisted Brønsted acid" concept for the superelectrophilic activation of 2-hydroxybenzo[e][1,2]oxaphosphinine 2-oxides (phosphacoumarins). The pivotal role is attributed to the tendency of the phosphoryl moiety to form hydrogen-bonded complexes, which enables the formation of dicationic species and increases the electrophilicity of the phosphacoumarin. This unmasks the reactivity of phosphacoumarins towards non-activated aromatics, while requiring only relatively non-benign trifluoroacetic acid as the reaction medium. [ABSTRACT FROM AUTHOR]

The electrophilic activation of various substrates via double or even triple protonation in superacidic media enables reactions with extremely weak nucleophiles. Despite the significant progress in this area, the utility of organophosphorus compounds as superelectrophiles still remains limited. Additionally, the most common superacids require a special care due to their high toxicity, exceptional corrosiveness and moisture sensitivity. Herein, we report the first successful application of the “Brønsted acid assisted Brønsted acid” concept for the superelectrophilic activation of 2-hydroxybenzo[e][1,2]oxaphosphinine 2-oxides (phosphacoumarins). The pivotal role is attributed to the tendency of the phosphoryl moiety to form hydrogen-bonded complexes, which enables the formation of dicationic species and increases the electrophilicity of the phosphacoumarin. This unmasks the reactivity of phosphacoumarins towards non-activated aromatics, while requiring only relatively non-benign trifluoroacetic acid as the reaction medium.

It was found that the reaction of 2-hydroxy-5,7,8-trimethyl-2H-1,2-benzoxaphosphinine 2-oxide with resorcinol and its derivatives as well as sesamol leads to the formation of phosphaneoflavanones in high yields. The obtained phosphaneoflavanones are precursors in the synthesis of novel unsymmetrical cage phosphonates. The structures of the obtained products were confirmed by IR spectroscopy, 1H, 13C NMR spectroscopy, and X-ray structural analysis. [ABSTRACT FROM AUTHOR]

A new approach has been developed to obtain 2H-1,2-oxaphosphorinine, which is a platform for the synthesis of asymmetric cage phosphonates. The structures of the obtained products were confirmed by IR spectroscopy, 1H, 13C NMR spectroscopy, and X-ray structural analysis. [ABSTRACT FROM AUTHOR]

The condensation of 2-ethoxyvinylphosphonic acid dichloroanhydride with 2,3,5-trimethylphenol in toluene in the presence of trifluoroacetic acid gives novel compounds of a 2-hydroxo-2-oxabenzo[е]-1,2-oxaphosphorinine series. [ABSTRACT FROM PUBLISHER]

Intramolecular hydroarylation using aryl alkynylphosphonates proceeds smoothly with a gold/silver catalyst in the presence of trifluoromethanesulfonic acid (TfOH) in the 6- endo mode, thus affording a unique synthetic method for phosphacoumarins having various functional groups, which could be a privileged structure and prevalent scaffold in phosphorus heterocycles. [ABSTRACT FROM AUTHOR]