Multicomponent reactions (MCRs), in which three or more reactants are connected sequentially in a one-pot reaction, have attracted considerable attention owing to high synthetic efficiency and the facile construction of complex organic molecules , , , , , , , , , , , , . 1,4-Dipolar cycloaddition, a subclass of MCRs, emerged as a convenient route towards the synthesis of a variety of six-membered N-heterocycles, exemplified by I (Fig. 1). The latter spiro-derivative is produced utilizing dimethyl acetylenedicarbxylate (DMAD), pyridine and N-methylisatin; herein, the 1,4-dipolar zwitter ion II ,  (Fig. 1) was suggested as transient intermediate arising from nucleophilic addition of the pyridine nitrogen onto DMAD. Interaction of various N-heteroarenes and dipolarophiles, together with DMAD, were successfully applied for attainment of the respective spiro-1,3-oxazino heterocycles, and the subject was reviewed .
Quite recently, we have applied this reaction in the synthesis of 1,3-oxazepino[7,6-b]indoles III (Fig. 1) utilizing imidazo[1,5-a]pyridines, DMAD and isatins . We sought it would be worthwhile to utilize other N-bridgehead-imidazo heterocycles (in placement of imidazo[1,5-a]pyridines) so as to widen the scope and applicability of this new reaction towards the synthesis of novel tricyclic and tetracyclic products.
Accordingly, the present work aims at the synthesis of a selected set of model 2-(quinolin-2-yl)-1,3-oxazepino[7,6-b]indoles 4a–d and dihydroacenaphtho[1,2-f][1,3]oxazepine 5, utilizing 1-phenylimidazo[1,5-a]quinoline, DMAD, and substituted isatins or acenaphthoquinone as illustrated in Schemes 1–3 (vide infra).
2 Results and discussion
The formation of compounds 4a–d most logically proceeds via the intermediacy of the spiro cyclo-adduct [B], produced via cycloaddition of the 1,4-dipolar zwitter ion [A] and the dipolarophilic keto group of the respective isatin (Scheme 2). Adducts [B] then suffer intramolecular skeletal rearrangement involving a cascade of bond-breaking and bond-making processes ([B]→[C]→[D]), leading to the respective end products as depicted in the postulated mechanism (Scheme 2). As a consequence, the dihdydroquinoline ring in spiro adducts [B] restores aromaticity whilst the spiro oxindole entity acquires the status of indolic system conjugated with the maleate moiety; such events represent the driving force for the conversion of the spiro adducts [B] into oxazepino[7,6-b]indoles 4a–d. This mechanism is essentially similar to that previously reported by us for related systems .
In its reaction with imidazo[1,5-a]quinoline and DMAD, acenaphthoquinone (an arene-vic-dione) followed an 1,4-dipolar cycloaddition path similar to that of isatins 3 and yielded the respective dihydroacenaphtho[1,2-f], oxazepine 5 as the end product (Scheme 3).
The new compounds 4a–d and 5 were characterized by MS and NMR spectral data. These data, detailed in the experimental section, are consistent with the suggested structures. Thus, the mass spectra display the correct molecular ion peaks for which the measured high resolution (HRMS) data are in good agreement with the calculated values. DEPT and 2D (COSY, HMQC, HMBC) experiments showed correlations that helped in the 1H and 13C signal assignments to the different carbons and their attached and/or neighboring hydrogens. For compound 4c, the carbons of the benzo-fused ring are readily identified by their doublet signals (with varying J values) originating from coupling with the nearby fluorine atom at C-5. Eventually, the structures of 4c (a representative of the present set) and 5 are confirmed by single-crystal X-ray crystallography (Figs. 2 and 3; vide infra).
The quinoline ring at C-2 might in part have interesting biological properties to the oxazepino[7,6-b]indoles 4a–d and dihydroacenaphtho[1,2-f], oxazepine 5. This follows from the fact that the quinoline nucleus occurs naturally in quinoline alkaloids with diverse biological activities .
2.2 Molecular structures of 4c and 5
Crystal structure determinations were performed to confirm the structures of 4c and 5. Crystal data and a summary of data collection and refinement parameters for 4c and 5 are given in Table 1, while selected sets of bond lengths and bond angles for 4c and 5 are provided in Tables 2 and 3, respectively. The molecular structures of 4c and 5 in the crystal are shown in Figs. 2 and 3.
Crystal data and structure refinement for compounds 4c and 5.
|Formula weight, g mol−1||565.14||656.66|
|Radiation/wavelength λ, Å||MoKa/0.71073|
|Density (calcd.), g cm−3||1.3554||1.321|
|Absorption coefficient μ(MoKa), mm−1||0.196||0.093|
|θ range data collection, °||3.18–29.36||5.944–58.712|
|Index ranges hkl||−20≤h≤13|
|Reflections collected||14 810||12 419|
|Independent reflections/Rint (F)2||6484/0.0217||7589/0.0445|
|Refinement method||Full-matrix least-squares on F2|
|Final R indices R1a/wR2b [I>2 σ(I)]||0.0488/0.1044||0.0915/0.2421|
|Final R indices R1a/wR2b (all data)||0.0846/0.1233||0.1493/0.3209|
|Goodness-of-Fitc on (F2)||1.009||0.991|
|Largest diff. peak/hole, e Å−3||0.19/−0.21||0.49/−0.45|
Bond Lengths (Å) and angles (°) for 4c.
|Bond lengths||Bond angles|
Bond lengths (Å) and angles (°) for 5.
|Bond lengths||Bond angles|
The crystal structure data of compounds 4c and 5 reveal slight deviations from mean planarity of the seven-membered rings. The most deviating atoms from planarity are the sp3-hydridized N3 and C2 atoms with values of −0.539 and 0.267 Å for compound 4c; a comparable deviation is also observed in compound 5 for the sp3-hydridized atoms N9 and C8 with values of −0.351 and 0.600 Å. A remarkable mutual interaction is observed in compound 4c between O4 (of the carbonyl group at C4) and C31 of the adjacent carbonyl ester as is evident from the close proximity of the two atoms, with a separation of only 2.58 Å, a value which is 0.640 Å less than the sum of their van der Waals radii. A comparable trend is also observed in compound 5 for the atoms O29 (of carbonyl group at C11) and C32 of the adjacent carbonyl ester, with a separation of only 2.597 Å, a value which is 0.623 Å less than the sum of their van der Waals radii. This interaction seems to force both carbonyl esters to acquire almost perpendicular arrangement to one another with a dihedral angle of 87.54° between C27–O4–O3–C30 and the C31–O5–O6–C34 planes for compound 4c, while for compound 5 the dihedral angle of 73.45° is observed between the planes C28–O29–O30–C31 and C32–O33–O34–C35.
3 Experimental section
Dimethyl acetylenedicarboxcylate (DMAD), quinoline-2-carbaldehyde, 5-methoxyisatin, 5-fluoroisatin, N-phenylisatin, acenaphthoquinone and dry dichloromethane were purchased from Acros. (Geel, Belgium). Melting points (uncorrected) were determined on a Gallenkamp electrothermal melting temperature apparatus (London, UK) in open capillary tubes. 1H, 13C NMR spectra, and 2D (COSY, HMQC, HMBC) experiments were recorded on a 500 MHz Bruker Avance-III spectrometer (Bruker, Daltonics, Bremen, Germany) with TMS as internal standard. Chemical shifts are expressed in δ units; J values for 1H–1H, 1H–19F, and 13C–19F coupling constants are given in Hertz. High-resolution mass spectra (HRMS) were measured using the electrospray ion trap (ESI) technique by collision-induced dissociation on a Bruker APEX-IV (7 Tesla) instrument (Karlsruhe, Germany).
3.1 N-methylisatin (3a) and 5-fluoro-N-methylisatin (3c)
These compounds were prepared by N-methylation of the appropriate 5-(substituted) isatin with iodomethane according to a reported procedure .
3.2 1-Phenylimidazo[1,5-a]quinoline (2)
This compound was prepared by the reaction of quinoline-2-carbaldehyde (in the presence of iodine, potassium bicarbonate and powdered molecular sieves 4 Å) according to a recently reported procedure .
3.3 General procedure for the preparation of 1,3-oxazepino[7,6-b]indoles 4a–d and dihydroacenaphtho[1,2-f][1,3]oxazepine 5
To a stirred solution of DMAD (0.71 g, 5.0 mmol) and substituted isatin or acenaphthoquinone (5.0 mmol) in anhydrous dichloromethane (15 mL) was added dropwise 1-phenylimidazo[1,5-a]quinoline (5.0 mmol) in dichloromethane (5 mL) under argon at room temperature. The reaction mixture was stirred for 24 h, the solvent then removed in vacuo, the residue soaked in n-hexane (10 mL), whereby the desired compound was produced as solid powder; It was then collected by suction filtration, air dried, and purified by chromatographic separation on silica gel plates, eluting with n-hexane-ethyl acetate (4:1, v/v).
3.3.1 (±)-Dimetyl 3-benzoyl-3,10-dihydro-10-methyl-2-(quinolin-2-yl)-2H-oxazepino[7,6-b]indolo-4,5-dicarboxylate (4a)
Orange solid; yield: 40%; m.p. 144–145°C. −1H NMR (500 MHz, CDCl3): δ=3.46 (s, 3H, 5-CO2CH3), 3.60 (s, 3H, 4-CO2CH3), 3.97 (s, 3H, N-CH3), 7.10 (pseudo t, 1H, 7-H), 7.30 (pseudo t, 1H, 8-H), 7.31 (d, J=6.9 Hz, 1H, 9-H), 7.36 (pseudo t, 2H, 3″-H/5″-H), 7.38 (t, J=7.2 Hz, 1H, 4″-H), 7.39 (d, J=8.5 Hz, 1H, 3′-H), 7.44 (d, J=7.2 Hz, 1H, 6-H), 7.52 (pseudo t, 1H, 6′-H), 7.56 (d, J=7.2 Hz, 2H, 2″-H/6″-H), 7.57 (pseudo t, 1H, 7′-H), 7.70 (d, J=8.4 Hz, 1H, 5′-H), 7.72 (d, J=8.7 Hz, 1H, 8′-H), 8.02 (d, J=8.5 Hz, 1H, 4′-H), 8.35 (s, 1H, 2-H) ppm.−13C NMR (125 MHz,CDCl3): δ=28.8 (CH3–N), 51.6 (5-CO2CH3), 52.4 (4-CO2CH3), 82.6 (C-2), 90.9 (C-5a), 108.9 (C-9), 117.9 (C-6), 118.7 (C-3′), 119.1 (C-5),121.9 (C-7), 122.1 (C-8), 123.8 (C-5b), 127.1 (C-5′), 127.4 (C-6′), 127.5 C-4′a), 128.0 (C-3″/5″), 128.1 (C-2″/6″), 129.6 (C-7′), 129.7 (C-8′), 131.2 (C-4″), 133.4 (C-9a), 135.4 (C-1″), 136.6 (C-4), 137.0 (C-4′), 147.0 (C-8′a), 152.6 (C-2′), 154.1 (C-10a), 163.3 (5-CO2Me), 166.8 (4-CO2Me), 171.1 (N–COPh) ppm.−HRMS (ESI): m/z=548.18348 (calcd. 548.18161 for C32H26N3O6, [M–H]−).
3.3.2 (±)-Dimetyl 3-benzoyl-3,10-dihydro-7-methoxy-10-methyl-2-(quinolin-2-yl)-2H-oxazepino[7,6-b]indolo-4,5-dicarboxylate (4b)
Orange solid; yield: 52%; m.p. 124–126°C. −1H NMR (500 MHz, CDCl3): δ=3.41 (s, 3H, 5-CO2CH3), 3.62 (s, 3H, 4-CO2CH3), 3.77 (s, 3H, 7-OCH3), 3.84 (s, 3H, N–CH3), 6.84 (d, J=8.7 Hz, 1H, 8-H), 6.90 (s, 1H, 6-H), 7.17 (d, J=8.7 Hz, 1H, 9-H), 7.31 (pseudo t, 2H, 3″-H/5″-H), 7.36 (t, J=7.0 Hz, 1H, 4″-H), 7.38 (d, J=8.5 Hz, 1H, 3′-H), 7.45 (pseudo t, 1H, 6′-H), 7.52 (d, J=7.3 Hz, 2H, 2″-H/6″-H), 7.56 (pseudo t, 1H, 7′-H), 7.70 (d, J=8.0 Hz, 1H, 5′-H), 7.73 (d, J=8.5 Hz, 1H, 8′-H), 8.03 (d, J=8.5 Hz, 1H, 4′-H), 8.33 (s, 1H, 2-H) ppm. −13CNMR (125 MHz,CDCl3): δ=28.9 (CH3–N), 51.4 (5-CO2CH3), 52.4 (4-CO2CH3), 55.8 (7-OCH3), 82.5 (C-2), 91.0 (C-5a), 102.7 (C-6), 109.5 (C-9), 110.5 (C-8), 117.9 (C-3′), 118.7 (C-5), 124.4 (C-5b), 127.1 (C-5′), 127.4 (C-6′), 127.5 (C-9a), 128.0 (C-3″/5″), 128.2 (C-4′a), 128.1 (C-2″/6″), 129.6 (C-8′), 129.7 (C-7′), 131.2 (C-4″), 135.5 (C-1″), 136.5 (C-4), 137.0 (C-4′), 147.0 (C-8′a), 152.6 (C-2′), 154.2 (C-10a), 155.6 (C-7), 163.3 (5-CO2Me), 166.8 (4-CO2Me), 171.1 (N–COPh) ppm. −HRMS (ESI): m/z=548.18348 (calcd. 548.18161 for C32H26N3O6, [M–H]−).
3.3.3 (±)-Dimetyl 3-benzoyl-3,10-dihydro-7-fluoro-10-methyl-2-(quinolin-2-yl)-2H-oxazepino[7,6-b]indolo-4,5-dicarboxylate (4c)
Orange crystal; yield: 47%; m.p. 196–198°C. −1H NMR (500 MHz, CDCl3): δ=3.41 (s, 3H, 5-CO2CH3), 3.62 (s, 3H, 4-CO2CH3), 3.84 (s, 3H, N–CH3), 6.94 (pseudo t, 1H, 8-H), 7.05 (dd, JH−H=2.0 Hz, JH−F=10.2 Hz, 1H, 6-H), 7.18 (dd, JH−H=8.5 Hz, JH−F=4.0 Hz, 1H, 9-H), 7.31 (pseudo t, 2H, 3″-H/5″-H), 7.37 (d, J=8.5 Hz, 1H, 3′-H), 7.39 (t, J=8.8 Hz, 1H, 4″-H), 7.43 (pseudo t, 1H, 6′-H), 7.52 (pseudo t, 1H, 7′-H), 7.53 (d, J=6.5 Hz, 2H, 2″-H/6″-H), 7.69 (d, J=7.9 Hz, 1H, 5′-H), 7.70 (d, J=8.2 Hz, 1H, 8′-H), 8.03 (d, J=8.5 Hz, 1H, 4′-H), 8.36 (s, 1H, 2-H) ppm. −13C NMR (125 MHz,CDCl3): δ=29.0 (CH3–N), 51.6 (5-CO2CH3), 52.4 (4-CO2CH3), 82.7 (C-2), 91.0 (C-5a), 105.0 (2JC−F=25.4 Hz, C-6), 109.6 (d,3JC−F=9.7Hz, C-9), 109.7 (2JC−F=25.5 Hz, C-8), 117.9 (C-3′), 119.3 (C-5), 124.4 (3JC−F=10.1 Hz, C-5b), 127.2 (C-5′), 127.4 (C-6′), 127.5 (C-4′a), 128.0 (C-3″/C-5″), 128.1 (C-2″/C-6″), 129.6 (C-7′), 129.8 (C-8′), 131.0 (C-9a), 131.3 (C-4″), 135.5 (C-1″), 136.1 (C-4), 137.1 (C-4′), 146.9 (C-8′a), 152.3 (C-2′), 154.7 (C-10a), 159.1 (1JC−F=236.4 Hz, C-7), 163.2 (5-CO2Me), 166.6 (4-CO2Me), 171.0 (N–COPh) ppm. −HRMS (ESI): m/z=548.18348 (calcd. 548.18161 for C32H26N3O6, [M–H]−).
Light-orange needle-like crystals suitable for X-ray crystallography were obtained by allowing a warm solution of 4c in ethyl acetate-n-hexane (1:1, v/v) to stand at r. t. for 2–3 days.
3.3.4 (±)-Dimethyl 3-benzoyl-3,10-dihydro-10-phenyl-2-(quinolin-2-yl)-2H-oxazepino[7,6-b]indolo-4,5-dicarboxylate (4d)
Orange solid; yield: 42%; m.p. 130–132°C. −1H NMR (500 MHz, CDCl3): δ=3.49 (s, 3H, 5-CO2CH3), 3.64 (s, 3H, 4-CO2CH3), 7.10 (pseudo t, 1H, 7-H), 7.18 (pseudo t, 1H, 8-H), 7.24 (d, J=8.4 Hz, 1H, 9-H), 7.35 (pseudo t, 2H, 3″-H/4″-H), 7.41 (t, J=7.2 Hz, 1H, 4″-H), 7.42 (d, J=8.2 Hz, 1H, 6-H), 7.44 (d, J=8.4 Hz, 1H, 3′-H), 7.49 (pseudo t, 1H, 6′-H), 7.58 (d, J=6.5 Hz, 2H, 2″-H/5″-H), 7.59 (pseudo t, 1H, 7′-H), 7.74 (d, J=7.4 Hz, 1H, 5′-H), 7.78 (d, J=8.3 Hz, 1H, 8′-H), 8.08 (d, J=8.4 Hz, 1H, 4′-H), 8.42 (s, 1H, 2-H) ppm. −13C NMR (125 MHz,CDCl3): δ=51.7 (5-CO2CH3), 52.5 (4-CO2CH3), 82.1 (C-2), 91.5 (C-5a), 110.2 (C-9), 118.0 (C-6), 118.7 (C-3′), 119.8 (C-5), 122.3 (C-8), 122.4 (C-7), 124.0 (C-5b), 126.9 (C-2‴/C-6‴), 127.1 (C-5′), 127.5 (C-6′), 127.6 (C-4′a), 127.6 (C-4‴), 127.8 (C-3″/5″), 128.1 (C-2″/6″), 128.6 (C-3‴/C-5‴), 129.6 (C-7′), 129.7 (C-8′), 131.3 (C-4″), 134.0 (C-9a), 134.9 (C-1‴), 135.4 (C-1″), 136.3 (C-4), 137.1 (C-4′), 146.9 (C-8′a), 152.3 (C-2′), 153.7 (C-10a), 163.3 (5-CO2Me), 166.8 (4-CO2Me), 171.0 (N–COPh) ppm. −HRMS (ESI): m/z=60 818 303 (calcd. 60 818 271 for C37H26N3O6, [M–H]−).
3.3.5 Dimethyl 9-benzoyl-8-(quinolin-2-yl)-8,9-dihydroacenaphtho[1,2-f][1,3]oxazepine-10,11-dicarboxylate (5)
Orange solid; yield: 34%; m.p. 177–179°C. −1H NMR (500 MHz, CDCl3): δ=3.53 (s, 3H, 5-CO2CH3), 3.62 (s, 3H, 4-CO2CH3), 7.31 (pseudo t, 2H, 3″-H/5″-H), 7.37 (t, J=7.2 Hz, 1H, 4″-H), 7.42 (pseudo t, 1H, 2-H), 7.43 (pseudo t, 1H, 6′-H), 7.47 (d, J=7.2 Hz, 1H, 1-H), 7.50 (d, J=8.5 Hz, 1H, 3′-H), 7.57 (d, J=7.5 Hz, 2H, 2″-H/6-H″), 7.58 (pseudo t, 1H, 7′-H), 7.69 (d, J=7.9 Hz, 1H, 5′-H), 7.71 (pseudo t, 1H, 5-H), 7.72 (d, J=7.8 1H, 8′-H), 7.78 (d, J=8.4 Hz, 1H, 3-H), 7.98 (d, J=8.0 Hz, 1H, 4-H), 8.00 (d, J=8.5 Hz, 1H, 4′-H), 8.12 (d, J=6.9, 1H, 6-H), 8.44 (s, 1H, 8-H) ppm. −13C NMR (125 MHz,CDCl3): δ=51.8 (10-CO2CH3), 52.4 (11-CO2CH3), 84.6 (C-8), 109.2 (C-11a), 118.6 (C-3′), 122.5 (C-1), 123.3 (C-6), 125.6 (C-3), 126.3 (C-11c), 126.5 (C-11), 127.1 (C-5′), 127.4 (C-6′), 127.5 (C-4′a), 127.9 (C-3″/C-5″), 128.1 (C-2″/C-6″), 128.1 (C-2), 128.3 (C-3a), 129.4 (C-8′), 129.7 (C-5), 130.7 (C-4), 131.2 (C-4″), 132.6 (C-6a), 135.3 (C-11b), 135.8 (C-1″), 136.6 (C-10), 137.2 (C-4′), 153.8 (C-2′), 162.8 (C-6b), 163.0 (11-CO2Me), 166.4 (10-CO2Me), 171.6 (N–COPh) ppm. −HRMS (ESI): m/z=567.15499 (calcd. 567.15616 for C35H23N2O6, [M–H]−).
Red needle-like crystals suitable for X-ray crystallography were obtained by allowing a warm solution of 5 in ethyl acetate-n-hexane (1:1, v/v) to stand at r. t. for 1–2 days.
4 Collection of X-ray diffraction data and structure analysis of compounds 4c and 5
Suitable single crystals of 4c (with approximate dimensions of 0.08×0.04×0.02 mm3) and 5 with approximate dimensions of 0.08×0.06×0.02 mm3 were epoxy-mounted on glass fibers. Data for 4c and 5 were then collected at room temperature (T=293 K) using an Oxford Calibur Diffractometer. Data were acquired and processed to give Shelx-format hkl files using CrysAlisPro software . Cell parameters were determined and refined using CrysAlisPro . A multiscan absorption collection was applied with maximum and minimum transmission factors of 1.000 and 0.929, and 1.000 and 0.893 for compounds 4c and 5, respectively. The structures were solved by Direct Methods and refined by full-matrix least-squares on F2 using all unique data . All non-hydrogen atoms were refined anisotropically with the hydrogen atoms placed in calculated positions and refined using a riding model.
CCDC 1917375 and 1952187 contain the supplementary crystallographic data for compounds 4c and 5, respectively. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre viawww.ccdc.cam.ac.uk/data_request/cif.
5 Supporting information
1H and 13C NMR spectra of representative compounds 4a (Figs. S1–S11), 4b (Figs. S12–S23), 4c (Figs. 24–S34), 4d (Figs. S35–S46) and 5 (Figs. S47–S58) are given as supplementary material available online (DOI: 10.1515/znb-2019-0150).
This research work has been supported financially by the Scientific Research Support Fund (SRSF/project number-Bas/2/13/2016) at Amman, Jordan.
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The online version of this article offers supplementary material (https://doi.org/10.1515/znb-2019-0150).