The 2,3-dihydrobenzofuran heterocyclic systems are found in various biologically active natural and pharmaceutical products of biological relevance such as Phalarine, Rocaglamide, and Furaquinocin A. The interest in the study of 2,3-dihydrobenzofurans is constantly increasing because of their numerous biological properties such as anti-tumor, anticancer, anti-tubercular, and anti-malarial activities. Different methods have been established towards the synthesis of 2,3dihydrobenzofurans involved via intra-and inter-molecular reactions. Besides, the 1,3-dihydroisobenzofuran structure has been identified as a fundamental nucleus in many natural products, bioactive compounds, and functional molecules (e. g., Pestacin, Isopestacin, Citalopram, Xylarinol B, Matriisobenzofuran, Thunberginol F7-O-β-D-glucopyranoside). On the other hand, 1,3-disubstituted isobenzofurans are powerful structural motifs with a wide range of biological activities, like anti-inflammatory, anti-histaminic, and anti-HIV. In the last few years, a decent number of diligent synthetic approaches have been demonstrated toward synthesizing 1,3-disubstituted isobenzofurans. This review focuses on the effective synthetic routes developed to construct 2,3-dihydrobenzofurans and 1,3-dihydroisobenzofurans and their applications in recent years.
An efficient and facile method for the regioselective synthesis of novel dihydrobenzo[a]fluorenes from readily accessible alkynols is presented. The current strategy triggers the formation of a dual C−C bond intramolecularly via Lewis acid catalysis under mild reaction conditions. Notably, secondary as well as tertiary alcohols bearing an alkyne moiety have been smoothly transformed into the corresponding products. As a result, novel tetracyclic dihydrobenzo[a]fluorenes have been accomplished using this approach.Article pubs.acs.org/joc
This report illustrates BF 3 •OEt 2 promoted intramolecular cascade cycloaromatization of 1,7-ynones toward synthesizing structurally diverse benzofluorene scaffolds. Remarkably, the present protocol promotes the formation of two consecutive C−C bonds intramolecularly and undergoes aromatization under mild reaction conditions to afford the tetracyclic benzo[a]fluorene frameworks. Besides, the formation of indenes was observed when 1-bromo-2-iodoarenes are relatively more electron-rich when compared with the one originating from the terminal arylacetylenes, under controlled conditions, wherein triple bond polarity has been just reversed due to the change of electronic effects exerted by the strong +M group of 1-bromo-2iodoarenes, which is in conjugation to the connected triple bond. The same concept to generate indenes has also been extended by using aliphatic alkyne tethered ynones. Further, it was noticed that 1,7-ynones bearing the more electron-rich 1-bromo-2-iodoarenes than the arene ring arriving from the terminal arylacetylenes lead to benzo[b]fluorenes, under thermodynamic conditions, instead of delivering the benzo[a]fluorenes. In addition, this method features metal-free conditions, easily accessible starting materials, operational simplicity, gram-scale synthesis, and a wide range of substrate scopes.
This article describes the development of a new aliphatic nitrile-template-directed remote meta-selective C−H olefin functionalization reaction of arenes. Remarkably, unlike the previous reports, this process is feasible at room temperature and enabled the formation of products with excellent regioselectivity. The present protocol encompasses a broad spectrum of substituted dihydrocinnamic acids and olefins, producing meta-C−H olefinated products (up to 96% yield). In addition, the efficacy of the present method has been showcased by the synthesis of various drug analogues (e.g., cholesterol, estrone, ibuprofen, and naproxen). Significantly, the robustness of meta-olefination was also demonstrated by gram-scale synthesis. The new nitrile-based meta-directing template, in particular, could be easily synthesized in two steps and recycled under mild conditions.
Coupling reactions stand amid the most significant reactions in synthetic organic chemistry. Of late, these coupling strategies are being viewed as a versatile synthetic tool for a wide range of organic transformations in many sectors of chemistry, ranging from indispensable synthetic scaffolds and natural products of biological significance to novel organic materials. Further, the usage of dual-catalysis in accomplishing various interesting cross-coupling transformations is an emerging field in synthetic organic chemistry, owing to their high catalytic performance rather than the usage of a single catalyst. In recent years, synthetic organic chemists have given considerable attention to hetero-dual catalysis, wherein these catalytic systems have been employed for the construction of versatile carbon-carbon [C(sp3)–C(sp3), C(sp3)–C(sp2), C(sp2)–C(sp2), etc.] and carbon-heteroatom (C-N, C-O, C-P, C-S, etc.) bonds. Therefore, in this mini-review, we are emphasizing recently developed various cross-coupling reactions catalysed by transition-metal dual-catalysis (i.e., using palladium and copper catalysts, and by omitting the reports on photoredox/metal catalysis).
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