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Mendeleev Communications Electronic Version, Issue 5, 1997 (pp. 169–212) Cycloaddition reaction of 3,4-dihydro-6,7-dimethoxyisoquinoline to pyrylium salts Dmitrii E. Tosunyan, Sergei V. Verin* and Evgenii V. Kuznetsov Research Institute of Physical and Organic Chemistry, Rostov State University, 344104 Rostov-on-Don, Russian Federation. Fax: +7 863 228 5667 The first example of cycloaddition to the 2 and 5 positions of 2,4,6-triphenylpyrylium has been observed.It is known that azomethines undergo cycloaddition reactions with benzo[c]pyrylium salts with the formation of dihydroisoquinolinium salts, whose ring includes a C–N fragment from azomethine.1,2 In contrast, interaction of monocyclic pyrylium salts with azomethines produce pyridinium salts, the same as those obtained from treatment of pyrylium salts with amines from azomethines.3,4 Unexpectedly we found that cyclic azomethine (3,4-dihydro- 6,7-dimethoxyisoquinoline 2) interacts by the cycloaddition not only with benzo[c]pyrylium salts 1a,b but also with triphenylpyrylium perchlorate 5.Treatment of the salt 1a with 2 in boiling DMF results in the formation of 55% of perchlorate 4a, separated from the reaction mixture by the addition of diethyl ether and crystallisation of the residue from ethanol.In the same way quinolizinium salt 4b was obtained in 45% yield. From our point of view, the mechanism of the formation of the salts 4a,b is the same as that for the reaction of benzo[c]pyrylium salts with azomethines of aromatic aldehydes.1 It includes cycloaddition of the C=N double bond to the 1 and 4 positions of the pyrylium ring, followed by cleavage of the ring with oxonium atom.Dihydroquinolizinium salts 3a,b, which have to be the products of this reaction, undergo oxidation under these reaction conditions, Scheme 1. At the same time, heating of 5 with 2 in DMF for 5 min produce 15% of the salt 7 and 45% of the salt 9, which were separated by means of column chromatography (Al2O3/CHCl3).The same reaction in ethanol yields, in addition to 15% of the salt 7 and 30% of 9, 20% of a deep-red coloured compound 10 which on treatment with perchloric acid undergoes reverse protonation into the dihydro salt 8. The most reasonable mechanism for this interaction involves cycloaddition of 3,4-dihydro-6,7-dimethoxyisoquinoline 2 to the pyrylium ring, as shown in Scheme 2, with the formation of O MeO MeO R O R N N MeO MeO N R O H H N MeO MeO R O OMe OMe 1a,b 2 3a,b 4a,b 1–4 a R = 3,4-(MeO)2C6H3 b R = OMe + ClO4 – Scheme 1 + ClO4 – + ClO4 – + ClO4 – O Ph Ph Ph O Ph Ph Ph N N Ph Ph OMe OMe N OMe OMe Ph Ph O Ph H H N Ph Ph OMe OMe Ph O N OMe OMe Ph O Ph Ph N MeO MeO 2 5 6 7 8 9 10 Scheme 2 + ClO4 – [O] –PhCHO H+ + ClO4 – + ClO4 – + ClO4 – + ClO4 – N Me MeO MeO Ph O Ph N Ph Ph OMe OMe + 11 12 7 + ClO4 – AcOH, HClO4, heat Scheme 3Mendeleev Communications Electronic Version, Issue 5, 1997 (pp. 169–212) key intermediate 6. Further elimination of benzaldehyde leads to the aromatic salt 7, while cleavage of the ring with oxonium atom results in the formation of dihydro salt 8, which then undergoes oxidation into the salt 9.The structures of the salts 4a,b and 7–9 were confirmed by means of elemental analysis, IR, 1H NMR spectroscopy and of compound 10 by mass spectroscopy.† In addition, the structure of 7 was confirmed by an alternative preparation. Heating of 1-methyl-3,4-dihydro-6,7-dimethoxyisoquinoline 11 with 1,3-diphenylprop-2-enone 12 in acetic acid for 12 h followed by 20 min heating in the presence of a double excess of perchloric acid gave 17% of dihydroquinolizinium salt 7.† Spectral data. 4a: 1H NMR (CDCl3) d: 3.08 (1H, t, J = 7.5 Hz, CH2), 3.20 (1H, t, J = 7.5 Hz, CH2), 3.37 (3H, s, OCH3), 3.82 (3H, s, OCH3), 3.86 (3H, s, OCH3), 3.90 (3H, s, OCH3), 4.03 (3H, s, OCH3), 4.10 (3H, s, OCH3), 4.68 (1H, t, J = 7.5Hz, CH2), 5.63 (1H, t, J = 7.5 Hz, CH2), 6.71–7.68 (7H, m, CHar), 9.23 (1H, s, H-1).IR (n/cm–1): 1660, 1606, 1115; mp 268 °C. 4b: 1H NMR (CF3COOD) d: 3.18–3.43 (2H, m, CH2), 3.05 (3H, s, OCH3), 3.75 (3H, s, OCH3), 3.80 (3H, s, OCH3), 3.90 (3H, s, OCH3), 4.05 (3H, s, OCH3), 4.65–4.87 (2H, m, CH2), 7.15 (1H, s, CHar), 7.40 (1H, s, CHar), 7.52 (1H, s, CHar), 7.70 (1H, s, CHar), 9.35 (1H, s, H-1). IR (n/cm–1): 1713, 1606, 1126; mp 245 °C. 7: 1H NMR (CDCl3) d: 3.06 (2H, t, J = 6.0 Hz, CH2), 3.92 (3H, s, OCH3), 3.96 (3H, s, OCH3), 4.42 (2H, t, J = 6.0Hz, CH2), 6.86–7.85 (14H, m, CHar). IR (n/cm–1): 1620, 1220, 1100; mp 251 °C. 8: 1H NMR (CDCl3) d: 2.45–2.70 (2H, m, CH2), 3.55 (3H, s, OCH3), 3.87 (3H, s, OCH3), 4.20–4.47 (2H, m, CH2), 5.72 (1H, d, J = 6.5 Hz), 6.05 (1H, d, J = 6.5 Hz), 7.07–7.67 (18H, m, CHar).IR (n/cm–1): 1687, 1663, 1100; mp 141 °C. 9: 1H NMR (CDCl3) d: 2.65–3.30 (2H, m, CH2), 3.26 (3H, s, OCH3), 3.81 (3H, s, OCH3), 4.30–4.65 (2H, m, CH2), 6.76–7.95 (18H, m, CHar). IR (n/cm–1): 1673, 1595, 1100; mp 192 °C. 10: Ms: 77 (70) Ph, 105 (100) PhCO, 394 (77) [M – PhCO], 496 (41) [M – 3H], 399 (19) M+. In conclusion, we have found the first example of a recyclisation reaction of monocyclic pyrylium salts via cycloaddition of the reagent to the 2 and 5 positions of the pyrylium ring.All well-known recyclisation reactions of monocyclic pyrylium salts5 are of the so-called ANRORC-type,6 e.g. the main steps in their mechanism involve the nucleophilic addition, ring opening and ring closure. References 1 S. V. Verin, D. E. Tosunyan, P.I. Zakharov, V. C. Shevtsov and E. V. Kuznetsov, Khim. Geterotsikl. Soedin., 1990, 1177 [Chem. Geterocycl. Compd. (Engl. Transl.), 1990, 26, 980]. 2 D. E. Tosunyan, S. V. Verin and E. V. Kuznetsov, Khim. Geterotsikl. Soedin., 1992, 1465 [Chem. Geterocycl. Compd. (Engl. Transl.), 1992, 28, 1249]. 3 G. N. Dorofeenko, E. A. Zvezdina and V. V. Derbenev, Zh. Org. Khim., 1973, 1079 [J. Org. Chem. USSR, 1973, 9, 1106]. 4 G. N. Dorofeenko, E. A. Zvezdina, V. V. Derbenev and Yu. A. Zhdanov, Khim. Geterotsikl. Soedin., 1974, 1036 [Chem. Geterocycl. Compd. (Engl. Transl.), 1974, 10, 902]. 5 A. T. Balaban, A. Dinculescu, G. N. Dorofeenko, G. W. Fisher, A. V. Koblic, V. V. Mezheritskii and W. Schroth, Pyrylium Salts. Synthesis, Reactions and Physical Properties, in Adv. Heterocycl. Chem., Academic Press, New York, 1982, Suppl. vol. 2. 6 H. C. Van der Plus, Accounts Chem. Res., 1978, 11, 462. Received: Moscow, 24th October 1996 Cambridge, 25th November 1996; Com. 7/05568D

ISSN:0959-9436     

出版商:RSC    

年代:1997

数据来源: RSC