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Photocatalyst-free visible light-enabled direct oxygenation of furan-tethered α-azidoketones was studied. The reaction yielded various products depending on the substituents, with isoxazoles forming as the major products. The findings suggest that singlet oxygen was generated during the reaction and reacted with α-azidoketones in a [4 + 2] fashion to yield endoperoxides, which rearranged in multiple ways to generate isoxazoles. Some of the synthesized isoxazoles were evaluated as α-glucosidase inhibitors, and three of them 5bi, 5bj, and 5blexhibited good activity with IC50values of 454.57 ± 29.34, 147.84 ± 2.28, and 272.58 ± 42.06 μM, respectively, when compared with the standard drug acarbose (IC50= 1224.33 ± 126.72 μM).

A tetra-functionalized pyrene precursor 4bis prepared using the Suzuki–Miyaura coupling of 1,3,6,8-tetrabromopyrene with N-Boc-2-pyrroleboronic acid. 4bdisplayed a blue emission with a high quantum yield (ϕF= 0.89). 4bis subjected to [3 + 2] Lewis acid-catalyzed condensation with 2,2′-bithiophene-dialcohol 5, affording a planar bis-N2S2internally linked with pyrene. The single-crystal X-ray structure of bis-N2S2revealed a planar conformation with all of the pyrrolic nitrogens and thiophenic sulfurs pointing toward the macrocyclic core. Further, the reduction of bis-N2S2was attempted in the presence of Zn/NH4Cl at room temperature in CHCl3. A sharp color change from pink to brown was observed presumably due to the formation of its reduced congener bis-N2S2–2H. However, the reduced species was found to revert back to its oxidized form over a period of 25 min in CHCl3. Density functional theory (DFT) studies reveal that the two monocyclic halves of bis-N2S2–2Hexhibit differences in aromaticity depending on amino and imino pyrroles present inside each individual core. Such a conversion was also monitored by ultraviolet–visible (UV–vis) absorption spectral studies, and the exact composition of bis-N2S2–2Hwas confirmed by High-resolution/mass spectrometry (HR/MS) analysis. Experimental and theoretical studies reveal a weak aromatic character of bis-N2S2due to the absence of global conjugation.

An acid-mediated and DMSO participant one-pot tandem synthesis of 3-substituted-1-aryl-1H-pyrazolo-[3,4- b]quinoline from readily available anilines and pyrazolones was achieved. This method enables regioselective construction of the valuable heterocycles under transition-metal and oxidant-free conditions in which DMSO acts as a methine source as well as solvent making this process an environmentally benign approach. A broad range of diversely substituted aryl amines and pyrazolines are successfully employed in this reaction to access a series of pyrazolo[4,3-c]quinolones through a novel cascade mechanism. Furthermore, the application and mechanistic studies of the present methodology also demonstrated.

Acid-catalyzed condensation of a newly prepared di-m-benzipentapyrrane with appropriate mono- and diheterocyclic dialcohols selectively produced stable di-m-benzihexaphyrins and di-m-benziheptaphyrins with only two meso-carbon bridges. Single-crystal X-ray diffraction analyses reveal planar conformation with slight distortion of bridged phenylene rings. Despite the presence of m-phenylene units interrupting the global delocalization, the presence of bithiophene units in di-m-benziheptaphyrins 3a–bexhibits altered optical features covering the entire visible region (ca. 250–720 nm), exhibiting a black dye property as a “metal-free” porphyrinoid.

We report the synthesis and characterization of two porphyrin arrays C6F5-PyZnDP and Mes-PyZnDP covalently linked by a pyrene moiety which differs from their substituents at their meso-positions. The key precursor bis-dipyrromethane linked with a pyrene bridge was prepared by the acid-catalyzed condensation of pyrene-1,6-dialdehyde with excess pyrrole. The synthesis of C6F5-PyZnDP was carried out via two different synthetic routes, with one being efficient over the other. Therefore, the superior route was employed for the synthesis of C6F5-PyZnDP and Mes-PyZnDP. Both the free base and metalated diporphyrins show bathochromically shifted absorption and intense red emission due to the extended π-conjugation through pyrene and porphyrins. The single-crystal X-ray structure reveals an orthogonal orientation of pyrene in between the two planar porphyrins and a slipped stacked packing arrangement in the crystal structure with large meso–meso distances. DFT analysis of both the ground state and the excited S1 state of the macrocycles indicates the difference in the HOMO and LUMO contribution in both the states arising from slight twisting from the mean orthogonal position in the excited state. Further, the Förster energy transfer (FRET) efficiencies from pyrene (donor) to the covalently linked Zn-porphyrins (acceptor) are estimated to be 85 and 91% for Mes-PyZnDP and C6F5-PyZnDP, respectively.

A new class of N-confused porphyrin 1embedded with a carbazole subunit was prepared via [3 + 1] acid-catalyzed condensation of appropriate precursors. 1underwent smooth metal complexation with Pd(II) and Cu(II) salts to provide the corresponding diamagnetic 1-Pdand paramagnetic 1-Cu, respectively. The single-crystal X-ray structure of 1-Pdis evident with a square-planar Pd-center through C–H activation of inverted pyrrole. Superconducting quantum interference device analysis combined with electron paramagnetic resonance (EPR) results provided insights into the paramagnetic nature of 1-Cu. Further, a ratiometric enhancement of near-IR fluorescence at 746 nm was found to be reversible upon adding CN–and F–ions. The solid-state structure of 1-Pdconfirms that the anionic species is due to NH deprotonation.