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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]

[Display omitted] Reactions between 4-(propargyloxy)benzaldehyde with anthracene-9-carbaldehyde oxime or pyrene-1-carbaldehyde oxime in the presence of chloramine T in ethanol lead to new isoxazole-containing derivatives of benzaldehyde. The subsequent acid-catalyzed condensation of these compounds with 2-methylresorcinol in chloroform/trifluoroacetic acid mixtures affords novel calix[4]resorcinols with anthaceneand pyrene-ended isoxazole-containing fragments as all– cis (rccc) and cis–trans–trans (rctt) diastereoisomers, their ratios being dependent on the CF 3 CO 2 H percentage in the medium. The crystal structures of pyrene-ended isoxazole-containing benzaldehyde and corresponding calix[4]resorcinol rctt isomer have been established by single crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

Presented herein is a novel synthesis of new 2-(quinolin-4-yl)-1,4-dihydroquinazoline systems 8 , in which the acid-catalyzed rearrangement of spiro[benzo[ e ][1,4]diazepine-3,4'-quinolin]-2(1 H )-ones generated in situ from 3-(2-aminophenyl)-5 H -benzo[ e ][1,4]diazepin-2(1 H )-ones 6 with acetone and alkylmethyl ketones has been realized as an important step. An attempt to synthesize isomeric 2-(2-aminophenyl)-5 H -benzo[ e ][1,4]diazepin-3(4 H )-one 6'a by hydrolysis of the corresponding N -{2-[5 H -benzo[ e ][1,4]diazepin-3(4 H )-on-2-yl]phenyl}acetamide 5'a led to a new heterocyclic system, 6-methyl-8,13-dihydro-13a H -quinazolino[4,3- b ]quinazolin-5-ium 13a-carboxylate 14 , as a result of an unexpected rearrangement. In addition, it is noteworthy that during the hydrolysis of N -{2-[5 H -benzo[ e ][1,4]diazepin-2(1 H )-on-3-yl]phenyl}acetamides 5 , the not previously described 14-dihydro-5 H -14,5a-(epimino[1,2]benzo)benzo[5,6][1,4]diazepin[2,1 -b ]quinazolin-6(7 H )-ones 7 were unexpectedly obtained.

A facile and direct intramolecular indolinone-quinolone rearrangement was developed for the synthesis of quinolino[3,4- b ]quinoxalin-6-ones from spiro[indoline-3,2'-quinoxaline]-2,3'-diones, which are readily available with use of isatines, malononitrile, and 1,2-phenylenediamines under quite mild conditions. This efficient approach provides excellent yields and could potentially be used for the construction of a diverse library of quinolino[3,4- b ]quinoxalin-6-ones for high-throughput screening in medicinal chemistry. The reaction mechanism is explored by extensive DFT calculations.