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Heterocyclic and fused heterocyclic compounds are ubiquitously found in natural products and biologically interesting molecules, and many currently marketed drugs hold heterocycles as their core structure. In this chapter, recent advances on Pd-catalyzed synthesis of heterocycles in ionic liquids (ILs) are reviewed. In palladium catalysis, ILs with different cations and anions are investigated as an alternative recyclable and environmentally benign reaction medium, and a variety of heterocyclic compounds including cyclic ketals, quinolones, quinolinones, isoindolinones, and lactones are conveniently constructed. Compared to the traditional methods, these new approaches have many advantages, such as environmentally friendly synthetic procedure, easy product and catalyst separation, recyclable medium, which make them have the potential applications in industry.

Cellulose with at least one of its dimensions less than or equal to 100 nm is termed as nanocellulose. It is a unique and promising natural material extracted from native cellulose and produced by certain microbial cells and cell-free systems. Nanocellulose has received immense consideration in last couple of decades owing to its abundance, renewability, remarkable physical properties, special surface chemistry, and excellent biological features (biocompatibility, biodegradability, and non-toxicity). Taking advantage of the structure and properties of nanocellulose, the current science of biomaterials aims at developing new and formerly non-existing materials with novel and multifunctional properties, in an attempt to meet current requirements in different fields such as biomedicine, the environment, energy, pharmaceutics, agriculture, food, etc. This chapter provides an overview of different synthesis methods of nanocellulose: mechanical approaches by applying high-pressure, grinding, crushing, sonication, and milling; chemical synthesis involving alkaline, acidic, oxidation, and enzymatic treatment; as well as by using bacteria and cell-free systems. It further discusses different morphological forms of nanocellulose including cellulose nanocrystals (CNCs), cellulose nanofibers (CNFs), bacterial nanocellulose (BNC), and cellulose produced by cell-free systems, in terms of their features such as chemical structure, macrostructural morphology, physico-mechanical properties, thermal and biological properties, rheology, optical behavior, and their interrelationships and applications.

Looking for sustainable synthetic methodologies, mechanochemistry as a new tool for one-step and two-step approaches for the synthesis of meso-substituted porphyrins was explored. The best results were obtained in a two-step procedure, under liquid-assisted grinding in the oxidation step using 2-methyltetrahydrofuran, an environmentally acceptable solvent, and MnO₂ as a heterogeneous oxidant. The sustainability was assessed using two sustainability metrics, E-factor and EcoScale, which allow comparison between procedures and methods.

Dihydroporphyrins or chlorins differ from porphyrins only by saturation of a peripheral double bond of the macrocycle. However, this small structural difference leads to a significant increase of the absorption band at approximately 650 nm, which makes them very interesting candidates for photodynamic therapy applications. The reduction of porphyrins bearing two, three or four pyridyl substituents with tin(II) chloride has been developed for the synthesis of dihydroporphyrins in yields of 15–73%. The reduction of 5-(aryl)-10,15,20-tris(2 or 4-pyridyl)porphyrin with tin(II) chloride dihydrate demonstrated good regioselectivity. Porphyrins with one meso-aryl bearing one electron-donating group (EDG) gave 5-aryl-10,15,20-tris(2- or 4-pyridyl)-17,18-dihydroporphyrins in 17–72% yield. Porphyrins with one meso-aryl bearing one or more electron-withdrawing groups (EWG) gave 5-aryl-10,15,20-tris(4-pyridyl)-17,18-dihydroporphyrins or 5-aryl-10,15,20-tris(4-pyridyl)-7,8-dihydroporphyrins in 15–21% yield and isobacteriochlorin. We have also proven the possibility of functionalizing these compounds to design new regioisomerically pure photosensitizers.

4-[4-(1-Methyl-1-penylethyl)phenoxy]- and 4,5-di-[4-(1-methyl-1-phenylethyl)phenoxy]phthalonitriles are obtained by nucleophilic substitution. Mono- and double-decker lutetium and erbium complexes of 2(3),9(10),16(17),23(24)-tetrakis- and 2,3,9,10,16,17,23,24-octakis-[4-(1-methyl-1-phenylethyl)phenoxy]phthalocyanines are synthesized based on the phthalonitriles. Synthesized complexes are studied spectrophotometrically.

Unsymmetrical metal-free phthalocyanine was synthesized through cyclotetramerization of 4-[2,6-dimethyl-4-(4-tert-butyl-phenylazo)phenoxy]phthalonitrile and 4-(hexylthio)phthalonitrile in the presence of lithium in n-pentanol, then metal-free phthalocyanine was obtained by acidification with acetic acid. Finally, metalation was achieved by refluxing metal-free phthalocyanine in n-pentanol in the presence of zinc (II) salt. The structure of synthesized phthalocyanine derivatives were characterized by using proton nuclear magnetic resonance, mass spectrometry, ultraviolet–visible spectroscopy, and Fourier transform infrared spectroscopy. The HOMO–LUMO energies were computed using density functional theory. The HOMO–LUMO energy difference is 2.28 eV. The calculated results were consistent with the experimental data. In addition, aggregation behaviors and general trends for photophysical properties of these phthalocyanine derivatives were studied in tetrahydrofuran. The emission intensities of these phthalocyanine derivatives were strongly quenched by 1,4-benzoquinone in tetrahydrofuran.

Our laboratory started research on tetraazaporphyrins in the middle of the 1970s. Before our works there was no information in the literature about coordination and ionization properties of these compounds, formation of their metal complexes or their state and behavior in proton-donating and proton-acceptor media. We carried out the first studies of the coordination and acid-base properties of unsubstituted tetraazaporphine [1], its octaphenyl [2] and tetra(tetramethylene)-[3] substituted derivatives. In this micro-review we summarize our works on the peripheral functionalization of unsubstituted porphyrazines and on their acid-base and coordination properties.

Five meso-tetraaryl open-chain pentapyrroles were synthesized and characterized as to their electrochemistry and protonation reactions in nonaqueous media. The investigated compounds are represented as (Ar)₄PPyH₃ where Ar = m,m-F₂Ph, p-BrPh, Ph, m,p,m-(OMe)₃Ph or p-MePh and were characterized by UV-vis and ¹H NMR spectroscopy, mass spectrometry and electrochemistry. Cyclic voltammetry was used to measure redox potentials, while protonation involving the conversion of (Ar)₄PPyH₃ to [(Ar)₄PPyH₅]²⁺ was monitored by UV-vis absorption spectroscopy. Equilibrium constants for proton addition were calculated using the Hill equation. One of the pentapyrroles was also structurally characterized. The electrochemical data, protonation constants and crystal structure were then compared with data for previously examined pentapyrroles and analyzed as a function of the solvent properties and nature of substituents on the meso-phenyl rings of the macrocycle.