O-Annulation Leading to Five-, Six-, and Seven-Membered Cyclic Diaryl Ethers Involving C–H Cleavage

Abstract

Cyclic diaryl ethers are present in multiple natural compounds, organic pollutants as well as in π-conjugated organic molecular materials. This short review aims at overviewing the main synthetic advances in the O-annulation methods for preparing five-, six-, and seven-membered rings through C–H cleavage.1 Introduction2 Five-Membered Rings: The Dibenzofuran (DBF) Motif2.1 Palladium-Catalysed C–H Activation2.2 Copper-Catalysed C–H Activation2.3 Non-CH Activation Oxidant-Mediated Cyclisation2.4 Light-Mediated Cyclisation2.5 Acid-catalysed C–O Cleavage/C–O Formation3 Six-Membered Rings: DBX, PXX, Xanthone, and Their Derivatives3.1 Dibenzoxanthene (DBX)3.2 Peri-Xanthenoxanthene (PXX)3.3 Xanthones3.4 Miscellaneous4 Seven-Membered Rings: Cularine5 Conclusion

HOMO Energy-Level Lifting in p-Type O-Doped Graphenoids: Synthesis of Electrochromic Alkoxy-Decorated Xanthenoxanthenes

“…Starting from commercially available 2,7dihydroxynaphthalene (compound 7 in Scheme 1), monohexylation was performed, followed by CuO-mediated oxidative C-C and C-O bond formation, to obtain derivative 1 with a modest 18% yield. By using the stepwise route, CuCl2/amine complex was used to get 7,7'-bis(hexyloxy)BINOL (11) in 50% yield, which was subsequently cyclised using CuI and PivOH in DMSO at 140 °C affording derivative 1 with an overall yield of Scheme 1 Scheme 1 Synthetic path for the preparation of PXX-(OHex)2. a) HexI, K2CO3, DMF, 100 °C, 34% (9), 64% (10); b) CuCl2, α-phenylethylamine, MeOH/CH2Cl2, r.t. 50% (11), 45% (12); c) CuI, PivOH, DMSO, 140 °C, 77% (1), 50% (2); d) CuO, PhNO2, reflux, 18% (1).…”

Oxygen‐Doped PAH Electrochromes: Difurano, Dipyrano, and Furano‐Pyrano Containing Naphthalene‐Cored Molecules

“…[64,65] Taking advantage of their low oxidation potentials, O-doped PAHs can be considered as one of the promising classes of electrochromic small molecules. Amongst all O-doped molecules, [66] those featuring furanyl, [67][68][69][70][71] pyranyl, [72][73][74] or oxepinyl [75,76] rings are of particular interest to the area of optoelectronics, [66] especially as p-type semiconductors. [67] One of the most well-known examples of an O-doped electrochrome can be found in the peri-xanthenoxanthene (PXX, Figure 1), [77,78] a well-known molecular p-type semiconductor that was one of the first pyranyl-conjugates to exhibit electrochromic properties (from yellow to blue).…”

O‐Doped Nanographenes: A Pyrano/Pyrylium Route Towards Semiconducting Cationic Mixed‐Valence Complexes

“…xanthenoxanthene (PXX), we expected that this protocol could also lead to isolated pyranyl rings, [17] that in turn could be oxidized into pyrylium cations (Fig. 1, bottom).…”

“…To favor solubility,a ll molecules were decorated with t-butyl groups (Scheme 1). Capitalizing on the oxidative Pummerer cyclization [16] of peri-xanthenoxanthene (PXX), we expected that this protocol could also lead to isolated pyranyl rings [17] which, in turn, could be oxidized to pyrylium cations (Figure 1, bottom). Interestingly,mixed-valence (MV) complexes could be formed in the solid state between the electron-donating pyranyl molecules and its cationic pyrylium derivatives,generating p-type organic semiconductors.…”