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Synlett 2005(6): 1036-1038  
DOI: 10.1055/s-2005-864806
LETTER
© Georg Thieme Verlag Stuttgart · New York

Unusual Double ‘O/N to N/O’ Recyclization of 5-Alkyl-7,8-dimethoxy-2-arylbenzo[d]pyrrolo[3,2-b]pyrylium Perchlorates into 5-Alkyl-7,8-dimethoxy-2-arylfuro[2,3-c]isoquinolines

Valery S. Tolkunova, Oleg V. Shishkinb, Roman I. Zubatyukb, Igor F. Perepichka*a,, Vladimir I. Dulenkoa
a L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, R. Luxemburg Str. 70, Donetsk 83114, Ukraine
e-Mail: i.f.perepichka@durham.ac.uk;
b Institute for Scintillation Materials, National Academy of Sciences of Ukraine, Lenina ave. 60, Kharkiv 61001, Ukraine
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Publication History

Received 21 January 2005
Publication Date:
23 March 2005 (online)

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Abstract

Novel unusual double recyclization of both pyrrole and pyrylium cores of 5-alkyl-7,8-dimethoxy-2-phenylbenzo[d]pyrrolo[3,2-b]pyrylium perchlorate by nucleophiles is described, which regardless of the nucleophile (ammonium carbamate, triethylamine, sodium acetate, HCl in methanol), results in 5-alkyl-7,8-dimethoxy-2-phenylfuro[2,3-c]isoquinoline. The structure of 5-methyl-7,8-dimethoxy-2-phenylfuro[2,3-c]isoquinoline was established from X-ray diffraction analysis.

Key words

recyclization - pyrylium salt - isoquinoline - ANRORC reaction - nucleophile

1

Currently at the Department of Chemistry, University of Durham, Durham DH1 3LE, UK.

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General Procedure for the Reaction of Perchlorates 1a-c with Nucleophiles. To the solution of ammonium carbamate (50 mmol) in MeOH (50 mL) 5-alkyl-7,8-dimethoxy-2-arylben-zo[d]pyrrolo[3,2-b]pyrylium perchlorate (1a-c, 5 mmol) [5] was added and the mixture was refluxed for 2 h. MeOH was removed in vacuo and H2O (50 mL) was added to the residue. After stirring for 20 min, the product was filtered off, washed with H2O and dried to afford compounds 2a, 2b, or 2c in 50%, 47% and 43% yields, respectively.
7,8-Dimethoxy-5-methyl-2-phenylfuro[2,3- c ]iso-quinoline ( 2a): colorless needles, mp 199-200 °C (from MeCN). 1H NMR (500 MHz, DMSO-d 6): δ = 2.88 (s, 3 H, CH3), 3.96 (s, 3 H, 7-OMe), 4.07 (s, 3 H, 8-OMe), 7.34 (t, 1 H, J = 7.8 Hz, C4′-H), 7.40 (s, 1 H, C6-H), 7.47 (t, J = 7.8 Hz, 2 H, C3′ and C5′-H), 7.56 (s, 1 H, C9-H), 7.69 (s, 1 H, C1-H), 7.91 (d, J = 7.8 Hz, 2 H, C2′ and C6′-H). MS (EI): m/z (%) = 319 (100) [M+]. Anal. Calcd for C20H17NO3: H, 75.22; H, 5.37; N, 4.39. Found: C, 75.32; H, 5.31; N, 4.45.
7,8-Dimethoxy-5-ethyl-2-phenylfuro[2,3- c ]isoquinoline ( 2b): colorless needles, mp 173-174 °C (from 2-PrOH). 1H NMR (500 MHz, DMSO-d 6): δ = 1.40 (t, J = 7.5 Hz, 3 H, CH3,), 3.30 (q, J = 7.5 Hz, 2 H, CH2), 3.96 (s, 3 H, 7-OMe), 4.02 (s, 3 H, 8-OMe), 7.40 (t, 1 H, J = 7.8 Hz, C4′-H), 7.52 (t, J = 7.8 Hz, 2 H, C3′ and C5′-H), 7.54 (c, 1 H, C6-H), 7.71 (c, 1 H, C9-H), 7.91 (d, J = 7.8 Hz, 2 H, C2′ and C6′-H), 7.96 (c, 1 H, C1-H). MS (EI): m/z (%) = 333 (100) [M+]. Anal. Calcd for C21H19NO3: C, 75.66; H, 5.74; N, 4.20. Found: C, 75.48; H, 5.65; N, 4.31.
7,8-Dimethoxy-5-methyl-2-(4-bromophenyl)furo[2,3- c ]isoquinoline ( 2c): colorless needles, mp 212-213 °C (from 2-PrOH). 1H NMR (500 MHz, DMSO-d 6): δ = 2.89 (s, 3 H, CH3), 3.96 (s, 3 H, 7-OMe), 4.01 (s, 3 H, 8-OCH3), 7.49 (s, 1 H, C6-H), 7.67 (s, 1 H, C9-H), 7.73 (d, J = 8.5 Hz, 2 H, C2′ and C6′-H), 7.82 (d, J = 8.5 Hz, 2 H, C3′ and C5′-H), 8.00 (s, 1 H, C1-H). MS (EI): m/z (%) = 397 (98, 79Br) [M+], 399 (100, 81Br) [M+]. Anal. Calcd for C20H16BrNO3: C, 60.32; H, 4.05; Br, 20.06; N, 3.52. Found: C, 60.48; H, 4.18; Br, 20.23; N, 3.38.

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Melting points were determined on a Kofler hot-stage apparatus and were uncorrected. The 1H NMR spectra were obtained on a Bruker DRX500 (500.13 MHz) spectrometer using dimethylsulfoxide-d 6 as a solvent. Chemical shifts (δ) are in ppm and J values are in Hz. Mass spectra (EIMS) were determined with FINNIGAN MAT; INCOS 50 mass spectrometer operating at ionization potential of 70 eV.

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The crystals of 2a are monoclinic, C20H17NO3, at 20 °C a = 9.892 (2), b = 12.452(3), c = 12.971 (3) Å, β = 94.25(2)°, V = 1593.4 (6) Å3, M r = 159.67, Z = 4, space group P21/n, d calc = 1.331 g cm-3, µ(Mo-Kα) = 0.090 mm-1, F(000) = 672. Unit cell dimensions and intensity of 2850 reflections (2686 unique, R int = 0.035) were measured using automatic four-circle ‘Siemens P3/PC’ diffractometer (graphite-monochromated Mo-Kα radiation, 2θ/θ-scan, 2θmax = 50°). The structure was solved by direct method using SHELX97 software [Sheldrick, G. M. SHELX97, PC Version. A system of computer programs for the crystal structure solution and refinement, Rev. 2, 1998]. The positions of the hydrogen atoms were located from difference maps of electron density and refined using riding model with Uiso = nUeq of non-hydrogen atom bonded with hydrogen atom given (n = 1.5 for methyl groups and n = 1.2 for remaining H atoms). The structure was refined by full-matrix least squares method using anisotropic thermal parameters for all non-hydrogen atoms. Final divergence factors are wR2 = 0.155 for 3001 reflections (R1 = 0.052 for 1827 reflections with F > 4σ(F), S = 0.971). The full tables of the atomic coordinates, bond lengths and bond angles have been deposited at the Cambridge Crystallographic Data Centre, CCDC No 198113.

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When appropriate amounts of Et3N or NaOAc or HCl were used instead of ammonium carbamate, compounds 2a-c were isolated in similar yields to that for the reaction with ammonium carbamate. In the case of HCl, pyrylium salt (1a-c) was dissolved in concd aq HCl (10 mL per 1 g of 1a-c) on heating, the solution was refluxed for 2 h, cooled down and acidified with aq NaHCO3 until neutral or slightly basic reaction. The precipitate was filtered off, washed with H2O and dried to afford compounds 2a-c in somewhat lower yields (30-35%).

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Tao, Y. T.; Bogza, S. L.; Perepichka, I. F., manuscript in preparation.