were obtained for the first time from 8-aminoquinolines using the Povarov reaction. Various oxidizing agents were shown to effect the elimination of the substituent at C(4) with subsequent aromatization of the tetrahydroquinoline fragment.The Povarov reaction (the acid-catalyzed [4+2] cycloaddition of electron-rich alkenes to N-arylazomethines) is commonly used for the synthesis of substituted tetrahydroquinolines and, judging from the rising number of publications, is now experiencing a rebirth of interest [1-3]. Nevertheless, there have been only a few examples of the preparation of 2-furyl-1,2,3,4-tetrahydroquinolines by this method [4][5][6] and there is only one example of the use of an 8-aminoquinoline in the Povarov reaction [7]. This paucity is related primarily to the acidophobic nature of the furan fragment and, secondarily, to passivation of the acid catalysts. The behavior of 2-furyltetrahydroquinolines in the presence of oxidizing agents has also not been studied extensively and apparently is complex.2 -Furyltetrahydroquinolines 2a,b, 3, and 4 used as the starting compounds in this work were obtained by the Povarov reaction from the corresponding furfurylideneanilines 1a,b and electron-rich alkenes (dihydrofuran, 3,4-2H-dihydropyran, and N-vinyl-2-pyrrolidone) in the presence of boron trifluoride etherate as described in our previous work [8]. The hydrogenated quinolines 2-4 are cis addition adducts.
The interactions between 4‐R‐substituted 2‐furyl‐1,2,3,4‐tetrahydroquinolines (synthesized by the Povarov reaction) and a number of alkenes have been investigated. Maleic, dibromomaleic, dichloromaleic, and citraconic anhydrides, as well as acryloyl, methacryloyl, crotonyl, and cynnamoyl chlorides were used as alkene components. It was shown that the initial N‐acylation of the tetrahydroquinolines was followed by a spontaneous [4+2]‐cycloaddition of an N‐acryloyl substituent to the furan ring. It was established that the intramolecular Diels–Alder reaction of furans is reversible, occurs stereoselectively as exo‐addition, and led to target epoxyisoindolo[2,1‐a]tetrahydroquinolines with moderate yields. Oxidation and aromatization of the synthesized products were carried out.
The title compound, C 21 H 18 N 2 O 4 , obtained as a racemate, contains a novel heterocyclic system, viz. isoindolo[1,2-c]-pyrrolo[1,2-a][1,4]benzodiazepine. The central diazepane ring has a distorted boat conformation with two phenylene-fused and one methine C atom deviating by 0.931 (1), 0.887 (1) and 0.561 (1) Å , respectively, from the mean plane of the rest of the ring. The -lactone ring has an envelope conformation, with the C atom opposite to amide bond deviating by 0.355 (1) Å from its plane. In the crystal, molecules form centrosymmetric dimers through pairs of C-HÁ Á ÁO hydrogen bonds.
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