Facile Synthesis of Tetrazolylchromonoids and Related Compounds

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<ul><li><p>Tetrazolylchromonoids 181 </p><p>Facile Synthesis of Tetrazolylchromonoids and Related Compounds Tamls Patonay* and Albert Ltvai </p><p>Department of Organic Chemistry, Kossuth University, H-4010 Debrecen, POB. 20. Hungary </p><p>Received February 18, 1993, revised form received April 13, 1993 </p><p>Einfache Synthese von Tetrazolylchromonoiden und verwandten Ver- bindungen </p><p>The reaction between the appropriate nitriles and tributyltin azide (TBTA) provides an easy and efficient method for the synthesis of the title com- pounds. Treatment of thiocyanate 9b with TBTA affords the alkylthio-sub- stituted tetrazole lob. </p><p>Die Umsetzung von Tributylzinnazid (TBTA) mit geeigneten Nitriles stellt eine einfache und ergiebige Methode zur Darstellung der Titelverbindun- gen dar. Die Behandlung des Rhodanids 9b mit TBTA fiihrt zum substitu- ierten Alkylthiotetrazole lob. </p><p>Owing to their well-known bioactivities, 5-substituted tetrazoles are especially important products in drug research. They possess, among oth- ers, antiallergic~2), anti asthma ti^^), leukotriene antagonist4). anti-hyperten- sive5), antithrombotic6), etc. activities. In the course of our work on the synthesis of biologically active chromonoids and 1 -thiochromonoids we aimed to work out a simple and convenient procedure for the preparation of their tetrazolyl derivatives. </p><p>1,3-Dipolar cycloaddition of azides to nitriles is by far the most widely used method to prepare 5-substituted tetrazoles but it is highly sensitive to the substituents of the substrate, the nature of cation in the azide source and the solvent). The procedure regarded as the best and used most fre- quently utilizes in sifu generated NI&amp;NJ in dimethylformamide (DMF)8) but other azide sources have also been d e ~ e l o p e d ~ . ~ ) to improve the poor yield of addition to sensitive nitriles. Though the usefulness of TBTA in the synthesis of tetrazoles has been recognizedlO), only scattered applica- tions have been published and the studied substrates, with the exceptions of some peptides), an enzyme inhibitor*) or an imidazole derivative) were quite simple. </p><p>Our interest in the synthesis of tetrazolylchromonoids and -thiochromonoids led us to investigate the reaction of TBTA with various heterocycles having a nitrile function linked directly to either the aromatic or heteroaromatic ring or bridged by an alkoxy chain. </p><p>Starting materials la-e, 3a-g, and 5 are known (cf. Experimental Part) while hitherto unknown compounds 9a,b were synthesized using standard procedures. Nitrile 9a and chloro compound 8 were obtained by alkylating 7- hydroxy-2-phenyl4H- 1 -benzopyran-4-one (7) with 5-chlo- rovaleronitrile and 1 -bromo-3-chloro-propane, respectively. Treatment of the latter product with KSCN in hot isobutyl methyl ketone afforded thiocyanate 9b in good yield. 2- Aryl-3-cyanobenzopyranones 12a,b were prepared by heat- ing of chloro compounds lla,b with CuCN in N-methyl-2- pyrrolidone ()I4) (Scheme 2). </p><p>Nitriles la-e, 3a-g, 5, 9a, and 12a,b were reacted with TBTA in refluxing 1,Zdimethoxyethane (DME) or diglyme and the corresponding tetrazoles were obtained (Scheme 1 and 2, Table 1). These solvents seem not to influence the yield, but diglyme allows shorter reaction times because of its higher boiling point. TBTA did affect neither the hetero- cycles nor the sensitive enone system of compound 3a-g. In </p><p>the case of these latter substrates the lack of any exo-endo rearrangement of the double clearly shows the mildness of the method. High yields of tetrazoles 13a,b are also noteworthy since treatment of nitrile 12a with NH4N3 in DMF8) led to total degradation of starting material whereas no reaction was observed using Al(N&amp; in THP). </p><p>Treatment of thiocyanate 9b with TBTA gave the expect- ed 5-tetrazolylthio-compound 10b in 69% yield demon- strating the versatility of TBTA. Similar transformation of simple thiocyanates using NH4N3 has been reported but yields varied within wide range^^,'^). </p><p>The products were characterized by their elemental analy- ses; IR- and H-NMR-spectroscopical data given in Tables 1 ,2 and in the Experimental Part. </p><p>In summary, tributyltin azide (TBTA) proved to be an ideal 1,3-dipole for the synthesis of tetrazoles linked to var- ious 0-, S-, or N-containing heterocycles giving products in higher yield or allowing the synthesis of compounds not available earlier. </p><p>This study was sponsored by the Hungarian Academy of Sciences (Grant No. OTKA- 1723) for which our gratitude is expressed. </p><p>Experimental Part </p><p>M.p.s: Boetius hot-stage apparatus, uncorrected.- IR specta: Perkin- Elmer 16 PC IT-IR spectrometer, KBr.- H-Nh4R spectra: Bmker WP 200 SY spectrometer, 200 MHz, SiMe4 as an int. standard.- EI mass spectra: VG 7035 GC-MS-DS instrument at 70 eV. </p><p>Compounds lai5, lbi9, lc15). ldI6), leI6), 3ato, 3d20), 3eI5), 3Pl), 3gI5), Sz2, Ila), and 12ai4 were prepared as described. Nitrile 3b24) and chlo- ride were synthesized using the methods of Kucharczyk ef and Merchant ct respectively. Tributlytin azide was prepared from tribu- tyltin chloride according to Kriecheldorf and Lepperr2). </p><p>2-(4-Cyunobenzylidenc)i~ol-3(2H)-one (3c) </p><p>3c was synthesized from indoxyl acetate and 4-cyanobenzaldehyde according as reporteda). Yield 37%; m.p. 270-273OC (2-butanone).- LR: V = 3368; 2218; 1688; 1612; 1596; 1486 1466; 1312; 1134: 752 cm..- C16H,$120 (246.3) Calcd. C 78.0 H 4.09 N 11.2 Found C 78.3 H 3.97 N 1 1.4. </p><p>Arch. Pharm. (Weinheim) 327,181-186 (1994) 0 VCH Verlagsgesellschaft mbH, D-69451 Weinheim, 1994 0365-6233/93/0303-0181 $5.00 + .25/0 </p></li><li><p>182 Patonay and Eva i </p><p>0 </p><p>la-e </p><p>0 </p><p>20-e </p><p>Ph Ph Ph </p><p>3a-g 4a-g </p><p>3 .4 I a b c d e f g CH, S NH CH, 0 0 S </p><p>Y bond bond bond CH, CH, CHPh CH, </p><p>0 </p><p>5 6 </p><p>Scheme 1: Reagents and conditions: i, Bu3SnN3, DME or diglyme, reflux. </p><p>7-(3-Chloropropoxy)-2-phenyl-4H-I-benzopyran-4-one (8) continued. After 62 h the inorganic salts were filtered off, the filtrate was </p><p>A mixture of benzopyranone 7 (3.57 g), 1-bromo-3-chloropropane (2.18 ml), K$O, (7.5 g) and acetone ( I 10 ml) was refluxed for 7 h. The inorga- nic salts were filtered off and the filtrate was evaporated in vacuo. Column chromatography of the crude product (silica, 0.063-0.2 mm, toluene-ethyl acetate (4:1), v/v) afforded pure 8 (1.96 g, 42%). m.p. 121-123C (hexane- ethyl acetate).- IR: V = 1634; 1602; 1446; 1378; 1248; 1178; 770 cm-'.- 'H-NMR (CDC13): 6 (ppm) = 8.16 (d, J = 9.5 Hz. IH, 5-H), 7.92 (m, 2H, 2'.6'-H), 7.53 (m. 3H, 3',4',5'-H), 7.01 (m, 2H, 6,8-H). 6.78 (s, lH, 3-H), 4.27 (t. J = 5.5 Hz, 2H, OCH2). 3.79 (t. J = 6.0 Hz. 2H, ClCH2), 2.82 (m, </p><p>(7). 279 (12). 238 (81), 237 (24). 210 (93), 209 (15). 152 (7), 136 (48), 119 </p><p>CI 1 I .3 Found C 69.0 H 4.63 CI 1 1.5. </p><p>2H. CH2C&amp;CH2).- MS: m/z = 316 ("CI-M+., 31%). 314 (M, 100). 286 </p><p>(7). 108 (23). 102 (15), 77 (13).- CI~H1-jC103 (314.8) Calcd. C 68.7 H 4.80 </p><p>7-(4-Cyanoburoxy)-2-phenyl-4H-I-benzopyran-4-one (9a) </p><p>A mixture of 7 (2.73 g), 5-chlorovaleronilrile (1.4 ml), K2C03 (2.0 g). KI (0.22 g) and 4-methyl-2-pentanone (50 ml) was refluxed for 32 h, then a further batch of 5-chlorovaleronitrile (0.7 ml) was added and heating was </p><p>concentrated and the residue was crystallized from hexane-ethyl acetate (1:l) to give 9a (2.26 g, 62%). m.p. 125-127C.- IR: 7 = 3060; 2950; 2244; 1632; 1602; 1454; 1376; 1360; 1250; 1172; 1090; 1026; 908; 830; 774; 692 cm-'.- 'H-NMR (CDCI,): 6 (ppm) = 8.15 (d, J = 9.5 Hz, IH, 5- H), 7.91 (m, 2H, 2',6'-H), 7.53 (m, 3H. 3'.4',5'-H), 7.00 (m. 2H, 6,8-H), </p><p>NCCHl), 1.87-2.1 I (m, 4H, CH2C&amp;C&amp;CH2).- C20H17N03 (319.4) Calcd. C75.2H5.37N4.39FoundC75.3H5.18N4.34. </p><p>6.78 ( s , lH, 3-H), 4.15 (t. J = 5.5 Hz, 2H, OCHI), 2.49 (t. J = 7.0 Hz, 2H, </p><p>7-(3-Thiocyana~opropoxy)-2-phenyl-4H-I-benzopyran-4-one (9b) </p><p>A mixture of 8 (705 mg), KSCN (450 mg) and 4-methyl-2-pentanone (12 ml) was refluxed for 17 h, then a second portion of KSCN (450 mg) was added and heating was continued. After 22 h the inorganic salts were filtered off, the filtrate was evaporated in vacuo and the residue was crystallized from hexane-ethyl acetate (1:1) to afford 9b (528 mg, 70%). m.p. 114.5-116C.- IR: V = 2932; 2152; 1628; 1598; 1448; 1370 1248; 1174; 1090; 1034; 828 c d . - 'H-NMR (CDC13): 6 (ppm) = 8.16 (d, J = 9.7 Hz, IH, 5-H). 7.92 (m, 2H, 2',6'-H), 7.56 (m. 3H, 3'.4',5'-H), 7.00 (m, </p><p>Arch. P h a m (Weinheirn) 327, 181-186 (1994) </p></li><li><p>Tetrazolylchromonoids 183 </p><p>'Q-owph NC "WPh _____) ill 0 0 </p><p>- O w p h 0 </p><p>a </p><p>0 </p><p>10a.b </p><p>CN 0 </p><p>1la.b 120. b 1311, b </p><p>11-13 I a b R I H OHe </p><p>Scheme 2: Reagents and conditions: i , Bu3SnN3. DME or diglyme, reflux; ii, Br(CH2)?CI. Me2C0, KzC03, reflux; iii, NC(CHz)4CI, MeCOBu', KzC03. KI, reflux; iv, KSCN, MeCOBu', reflux; v, CuCN, NMP, reflux. </p><p>Table 1: Synthesis conditions and physical constants for tetrazoles 2,4,6, 10, and 13. . Anal ysls% </p><p>Compound H.P. Yleld Reaction time Overall Calcd. Found C H N formula C H N OC x h </p><p>2aa </p><p>2ba </p><p>2ca </p><p>2da </p><p>2ea </p><p>4aa </p><p>4ba </p><p>4ca </p><p>272-276 </p><p>263-267 </p><p>285-288 </p><p>239-242 </p><p>143-145 </p><p>270-271 </p><p>259-262 </p><p>283-286 </p><p>75 1.0 </p><p>82 1.2 </p><p>84 2.5 </p><p>82 1.0 </p><p>66 1.5 </p><p>26 3.0 </p><p>48 4.5 </p><p>78 1.0 </p><p>C17n12N402 (304.3) </p><p>C23H16N402 (380.4) </p><p>C17H12N40S (320.4) </p><p>C23H16N405 (396.5) </p><p>C23H16N403s (428.5) </p><p>C17H12N40 (288.3) </p><p>C16H10N40S (306.4) </p><p>C16Hl lNSO (289.3) </p><p>67.1 3.97 18.4 67.2 3.89 18.4 </p><p>72.6 4.24 14.7 72.8 4.18 14.6 </p><p>63.7 3.77 17.5 63.9 3.81 17.4 </p><p>69.7 4.07 14.1 69.5 4.11 14.2 </p><p>64.5 3.76 13.1 64.6 3.72 13.0 </p><p>70.8 4.19 19.4 70.7 4. 14 19.2 </p><p>62.7 3.29 18.3 62.6 3.22 18.2 </p><p>66.4 3.83 24.2 66.4 3.79 24.3 </p><p>Arch. Pharm. (Weinheim) 327, 181-186 (1994) </p></li><li><p>184 Patonay and U v a i </p><p>Table 1: continued </p><p>4da 250-260 45 3.0 </p><p>4ea 253-256 39 1.2 </p><p>atb 255-260 54 36.0 </p><p>4ga 233-236 30 1.5 </p><p>6b 228-231 72 27.5 </p><p>iOaa 147-149 87 1.0 </p><p>loba 180-182 35 3.0 </p><p>13ab 251-254 53 6.5 </p><p>13bb 259-261 67 10.0 </p><p>'Reaction solvent: aDiglyme and bDME </p><p>C18H14N00 (303.3) </p><p>C17HI 2N402 (304.3) </p><p>C23H16N402 (375.4) </p><p>C17HIZN40S (320.4) </p><p>'1 gH1 2N402 (292.3) </p><p>C20H18N103 </p><p>C19H16N103S </p><p>ClbHION.02 </p><p>(362.4) </p><p>(380.4) </p><p>(290.3) </p><p>C17H12N403 (320.3) </p><p>71.5 4.66 18.5 71.2 4.58 18.2 </p><p>67.1 3.97 18.4 67.3 3.89 18.3 </p><p>72.6 4.24 14.7 72.5 4.19 14.9 </p><p>63.7 3.77 17.5 63.6 3.72 17.5 </p><p>65.7 4.14 19.2 65.7 4.19 19.3 </p><p>66.3 5.01 15.5 66.5 5.04 15.3 </p><p>60.0 4.24 14.7 59.7 4.27 14.5 </p><p>66.2 3.47 19.3 66.4 3.51 19.2 </p><p>63.7 3.77 17.5 63.5 3.71 17.6 </p><p>Table 2: IR and 'H-NMR spectroscopic data for tetrazoles 2,4,6, 10, and 13. </p><p>Compound v Icn-'l Y X </p><p>(KBrl </p><p>2a </p><p>2b </p><p>2c </p><p>2d </p><p>2e </p><p>4a </p><p>4b </p><p>4c </p><p>3020. 2926. 2866. 1622, 1598. 1566, 1466. 1354, 764 </p><p>3030, 2924, 2866. 1618, 1554, 1466, 1394. 1124, 759. 698 </p><p>3024, 2926. 2868, 1616. 1576, 1558. 1500, 1438. 1382. 1070. 744 </p><p>3056, 2924. 2864. 1614. 1586, 1576. 1540, 1494, 1438. 1344, 750, 698 </p><p>3064, 1662. 1618. 1496. 1440, 1308, 1156, 1126, 745. 700 </p><p>3070, 3032. 2922, 1680, 1622. 1328. 1296, 1272, 1094, 958, 746 </p><p>3088, 3066. 2922, 2870, 1682, 1656, 1590, 1566, 1450, 1284. 1066. 683 </p><p>3382, 3064. 2924. 2866. 1692, 1628, 1594, 1488, 1470. 1316, 1136, 750 </p><p>8.48(s. lH, 2-HI. 8.04 (dd, J = 8.512 Hz, lH, 5-H), 7.96(d, J = 8.8 Hz. 2H, 3",5"-H), 7.80(m, lH, 7-HI, 7.42-7.69(m, 2H, 6.8-H), 7.54 (d, J = 8.8 Hz, 2H, 2",6"-H). 3.83(s, ZH, CHZ) </p><p>8.08(dd. J = 9A.8 Hz, lH, 5-HI. 7.88(d. J = 8 Hz, 2H, 3".5"-H).7.82 (m. 1H. 7-HI, 7.47-7.71 (m, 7H, 6.8-H Phl, 7.30(d. J = 8 Hz. 2H. 2",6"-H), 3.92 (5. 2H. CHZI 8.38(dd, J = 8.8/2 Hz. lH, 5-HI. 8.30(s. lH, 2-H), 7.96(d, J 8.1 Ht, 2H. 3".5"-H). 7.88(dd, J = 8.6/1.6 Hz. 1H. 8-HI, 7.55- 7.77(n, 2H. 6.7-HI, 7.51(d. J = 8.1 Hz, 2H. 2",6"-H), 4.01(~, 2H. CH2) </p><p>8.39(dd, J = 8.2/1.5 Hz. 1H. 5-HI. 7.60- 7.95(n, 3H. 6.7,8-H), 7.85(d. J = 8.4 Hz. 2H. 3".5"-H). 7.53(m, 5H, Phl, 7.20(d, J = 8.4 Hz, 2H, 2",6"-H), 3.97(s. 2H. CHZ) </p><p>8. 19(ovsr1spp1ng dd, 2H. 5,8-H1, 7. 91-8. 10 (m. 2H. 6.7-H), 7.89(d. J = 8.4 Hz. 2H. 3". 5"-HI. 7.48-7.63(m, 5H, Ph). 7.24(d. J = 8.4 Hz. 2H. 2 " . 6"-H), 3.80(~, ZH, CH2) 8.18(d, J = 8.5 Hz, ZH, 3",5"-H), 8.03(d, J = 8.5 Hz. 2H, 2",6"-H). 7.84(dd. 1H. J = 7.6A.5 Hz. 4-HI, 7.67-7.79(1. 2H, 6.7-HI. 7.62(s, lH, pCH-1, 7.51(m, lH, 5-HI, 4.22 (s, 2H, 3-CH2) </p><p>8.22(d, J = 9.2 Hz. 2H. 3",5"-H). 8.01(d. J = 9.2 Hz, 2H, 2",6"-H). 7.99(s, 1H. =CH-), 7.91(dd. J = 9/13 Hz. lH, 4-HI, 7.72-7.89(m. 2H. 6,7-H), 7.45cm. lH, 5-H) </p><p>lO.OO(s. 1H. 1-NH). 8.12(d, J = 8.8 Hz. 2H, 3".5"-H), 7.94(d, J = 8.8 Hz. 2H, 2",6"- -HI, 7.51-7.66(m. 2H. 4,6-H), 7.18(dd, J = 8.811.6 Hz. 1H. 7-HI. 6.96(m. 1H. 5-HI. . . 6.69(s. 1H. =&amp;-I </p><p>Arch. Pharm. (Weinheim) 327, 181-186 (1994) </p></li><li><p>Tetrazol ylchromonoids </p><p>Table 2: continued </p><p>185 </p><p>4d </p><p>4e </p><p>4I </p><p>4g </p><p>6 </p><p>1 Oa </p><p>1 Ob </p><p>13a </p><p>13b </p><p>2943, 2850, 2728. 1670. 1604. 1432. 1318, 1298. 1250. 1226, 948. 754. 742 </p><p>3060. 2926. 2864. 1666. 1608, 1590. 1478. 1466. 1330. 1314. 1218. 1026. 992. 750 </p><p>3062, 2922, 2862. 1670. 1608, 1464. 1308, 1214, 998. 756, 700 </p><p>3092, 1650, 1436, 1068. </p><p>3020, 1652. 1228, </p><p>2952. 1558. 1252, </p><p>3064, 1586, 1244. </p><p>3063. 1396, </p><p>3230. 1472, 764 </p><p>3048. 2930, 2872. 1598. 1576, 1456. 1298. 1210. 1130. 964. 854, 760 </p><p>2926, 2868, 1688. 1604, 1468, 1316, 1066, 770 </p><p>2868. 1628, 1586, 1450, 1382, 1366, 1176. 776 </p><p>2934, 2884, 1626. 1566. 1448. 1382, 1178, 1028. 774 </p><p>1646. 1627. 1446, 1362, 1042, 745 </p><p>1536, 1612, 1504. 1262, 1180. 1044, </p><p>8. ll(d, J = 9 Hz, 2H. 3",5"-H). 7.97(dd, J = 8.5/1.7 Hz. lH, 8-H). 7.78(d. J = 9 Hz, 2H, 2".6"-H), 7.74(s, 1H. =CH-1, 7.60(m, 1H. 6-HI, 7.35-7.48(m. 2H. 5.7-HI. 3.12(rn, 2H, 4-H), 2.97(m. ZH, 3-H) 8.14(d. J = 8.8 Hz. 2H. 3",5"-Hl, 7.90(dd, J = 7.712 Hz, 1H. 5-H), 7.79(s, lH, zCH-1, 7.69cd. J = 8.8 Hz. 2H. 2",6"-H). 7.61 (n, lH, 7-HI. 7.02-7.20(a, 2H. 6.8-H), 5.48 (AA', 2H. 2-H) </p><p>8. 1O(d. J = 8.5 Hz. 2H, 3",5"-H), 8.09(s. lH, 4 - 1 . 7.82(dd. J = 8.112 Hz. 1H. 5-HI. 7.64(d, J = 8.5 Hz, 2H, 2",6"-H). 7.58(rn, 1H. 7-HI. 7.32-7.48(m. 5H. Ph). 7.02-7.12 (m, 2H. 6.8-H), 6.82(5, lH, 2-HI </p><p>8.15(d. J = 8.9 Hz, ZH, 3".5"-H). 8.08(dd, J = 8.W1.8 Hz,lH. 5-HI, 7.77(d, J a 8.9 Hz. 2H, 2",6"-H), 7.69(~, 1H. zCH-1, 7.30- 7.58(m. 3H, 6.7,8-H), 1.30(~. 2H. 2-H) </p><p>8.14(d, J = 9 Hz, 2H, 3".5"-H). 7.88-7.79 in. 3H. 5,2",6"-H), 7.66(m. lH, 7-HI. 7.16 rn. 2H. 6.8-H). 5.83(ABX, 1H. 2-H. J = </p><p>13.2 Hz, JBx = 3.1 Hz), 3.32fABX. 1H. 3ax-H, JAB = 17.0 Hz. JAx * 13.2 Hz), 2.94 (ABX. JAB = 17.0 Hz. JBx = 3.1 Hz, 1H. </p><p>A X </p><p>3.k"-H) </p><p>8.10frn. 2H, 2'.6'-H), 7.95(d, IH, 5-HI, 7.60trn. 3H. 3',4',5'-H), 7.33(d. J = 2.6 Hz, 1H. 8-HI. 7.08(dd, J = 9.4/2.6 Hz, 1H. 6-H), 6.97(~, lH, 3-HI. 4.20(t, J = 6.6 Hz. 2H. OCH 1, 3.01(t, J * 7.2 Hz. 2H, CH2 Tet), 1.88(rn, 4H. OCH2(CH2I2CH2Tet) </p><p>8.08(n. 2H. 2'.6'-H1, 7.96(d, J = 9.4 Hz, lH, 5-HI. 7.60(m. 3H. 3',4',5'-H), 7.32(d, J = 1.9 Hz. 1H. 8-HI. 7.08(dd. J = 9.411.9 Hz, 1H. 6-H). 6.98(s, lH, 3-HI, 4.28(t, J = 6.5 Hz. 2H, OCH 1, 3.45(t. J = 7.2 Hz. 3H. SCH2). 2.22(m, 2H. OCH2CH2CH2S) </p><p>8.14(dd. J = 811.6 Hz. 1H. 5-HI. 7.93(rn. 1H. 7-HI. 7.82(dd. J = 8.1/1.5 Hz, 1H. 8-H). 7.61(m, 1H. 6-HI. 7.38cd. 2H. J = 9.4 Hz. 2',6'-H). 7.01(d, 2H, J = 9.4 Hz, 3',5'-H), 3.81(s, 3H, M e ) </p><p>2H. 6,8-H), 6.79 (s. IH, 3-H). 4.27 (t. J = 5.8 Hz, 2H, OCHZ), 3.23 (t. J = 7.3 Hz, 2H, SCH2), 2.41 (m, 2H, CH2CY2CH2).- C,9H,5N03S (337.4) Calcd. C 67.6 H 4.48 N 4.15 S 9.50 Found C 67.2 H 4.44 N 4.02 S 9.71. </p><p>3-Cyano-2-(4-methoxyphenyl)-4H-l-beniopyran-4...</p></li></ul>