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Synlett 2008(20): 3213-3215  
DOI: 10.1055/s-0028-1087242
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Synthesis of Chlorins Extended by Highly Substituted Double Bonds

Frank Dullweber, Franz-Peter Montforts*
Institut für Organische Chemie, FB2, Universität Bremen, Leobener Straße NW2C, 28359 Bremen, Germany
Fax: +49(421)2183720; e-Mail: mont@chemie.uni-bremen.de;
Further Information

Publication History

Received 5 September 2008
Publication Date:
24 November 2008 (online)

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Abstract

Chlorins with highly substituted exocyclic double bonds extending the chromophoric system were synthesized starting from the readily accessible oxochlorin. After sulfurization of the keto function of oxochlorin 7 the formed thioketo chlorin 8 underwent Barton olefination with diazo compounds.

Key words

chlorins - Barton olefination - diazo compounds - extended chromophore

    References and Notes

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10

Procedure for the Preparation of the Chlorin Thioketone 8
Diethylenglycol dimethyl ether (5 mL) was added by a syringe to a mixture of 7 (76.9 mg, 0.155 mmol) and Lawesson’s reagent (96.6 mg, 0.239 mmol) placed in a flask equipped with a reflux condenser and a septum. The mixture was stirred for 2.5 h at 150 ˚C under argon. After cooling to r.t. the mixture was transferred by a small volume of CH2Cl2 into a 50 mL round-bottom flask, and the solvent was removed at 80 ˚C in high vacuum by Kugelrohr distillation. The residue was chromatographed on silica gel with a slice of 2 cm alumina on top with CH2Cl2-PE (8:2). The light-green main fraction was collected and the solvent was removed in vacuo. After isothermic crystallization from CH2Cl2-n-pentane 8 (73.9 mg, 0.145 mmol, 93.5%) was obtained.

11

Typical Procedure for the Preparation of Chlorin Derivatives 9-11
Compound 8 (96.3 mg, 0.188 mmol) and 9-diazofluorene (72.3 mg, 0.376 mmol, 2 equiv) were dissolved under argon in 13 mL of anhyd THF. After stirring for 30 min at r.t. the reaction mixture was refluxed for 60 min. Then, tris(2-cyanoethyl)phosphine (72.6 mg, 0.376 mmol) was added and refluxing was continued for further 3 h. The reaction mixture was diluted with CH2Cl2 and the organic layer was washed with H2O (50 mL). The organic extract was dried by filtration over cotton wool and evaporated in vacuo. The residue was chromatographed over alumina (activity II-III) first with PE and then with CH2Cl2-PE (1:1) giving a crude product which was again chromatographed on silica gel with CH2Cl2-PE (1:1) to yield after evaporation of the solvent the light-green product. Isothermic crystallization from chloroform-n-pentane yielded chlorin 11 (71.8 mg, 0.112 mmol, 60%).

12

All compounds show correct spectroscopic and analytic data.

Selected Spectroscopic and Analytic Data for Compounds 8-11
Compound 8: mp >350 ˚C. TLC: silica gel, CH2Cl2-PE (8:2): R f  = 0.74. ¹H NMR (360 MHz, CDCl3): d = 1.93 (s, 6 H, 3-CH3), 3.16, 3.17, 3.19, 3.21, 3.22 (5 s, 18 H, 7-, 8-, 12-, 13-, 17-, 18-CH3), 8.57, 9.13, 9.19, 9.81 (4 s, 4 H, 5-, 10-, 15-, 20-H). UV/Vis (CHCl3): lmax (lg e) = 354 mm (4.586), 400 (4.665), 454 (4.652), 551 (4.040), 591 (4.044), 690 (4.605). IR (KBr): 1222 cm-¹ (s, n, C=S). MS (EI, 70 eV, 286 ˚C): m/z (%) = 514 (10), 513 (17), 512 (47), 511 (33), 510 (100) [M(58Ni)+], 497 (25), 496 (19), 495 (51) [M+ - CH3], 480 (38) [M+ - 2 CH3], 465 (11) [M+ - 3 CH3]. HRMS: m/z calcd for C28H28N4S58Ni: 510.13882; found: 510.13907. Anal. calcd for C28H28N4SNi + 0.1 CH2Cl2: C, 64.93; H, 5.45; N, 10.78; S, 6.17. Found: C, 64.97; H, 5.41; N, 10.5; S, 6.26.
Compound 9: mp >350 ˚C. TLC: silica gel, CH2Cl2-PE (1:2): R f  = 0.63. ¹H NMR (360 MHz, CDCl3/20 mL pyridine-d 5): d = 1.89 (s, 6 H, 3-CH3), 3.13, 3.14, 3.19, 3.21, 3.22 (5 s, 18 H, 7-, 8-, 12-, 13-, 17-, 18-CH3), 5.75 (s, 1 H, 2-CH), 6.46 (s, 1 H, 2-CH), 8.00, 8.53, 8.61, 8.96 (4 s, 4 H, 5-, 10-, 15-, 20-H). UV/Vis (CHCl3): lmax (lg e) = 401 nm (4.980), 577 (4.102), 624 (4.638). MS (EI, 70 eV, 255 ˚C): m/z (%) = 495 (13), 494 (39), 493 (26), 492 [84, M(58Ni)+], 479 (44), 478 (40), 477 (100) [M+ - CH3], 476 (14), 475 (12), 461 (12), 246 (11), 238 (11), and fragment ions of lower mass. HRMS: m/z calcd for C29H30N4 58Ni: 492.18220; found: 491.18240.
Compound 10: mp >350 ˚C. TLC: silica gel, PE-EtOAc (9:1): R f  = 0.41. ¹H NMR (360 MHz, CDCl3/20 mL pyridine-d 5): d = 1.74 (s, 6 H, 3-CH3), 2.54, 3.03, 3.07, 3.15, 3.16 (5 s, 18 H, 7-, 8-, 12-, 13-, 17-, 18-CH3), 7.04-7.17 (m, 4 H, aryl H), 7.41-7.55 (m, 4 H, aryl H), 7.88, 8.01, 9.01, 9.05 (4 s, 4 H, 5-, 10-, 15-, 20-H). UV/Vis (CHCl3): lmax (lg e) = 415 nm (4.959) 556 (4.203), 645 (4.647). MS (DCI, positive, NH3): m/z (%) = 649 (10), 648 (24) 647 (54), 646 (55), 645 (100) [MH+]. MS (DCI, negative, NH3): m/z (%) = 648 (10), 647 (20), 646 (47), 645 (43), 644 (99) [M-], and fragments of lower mass, 96 (100). HRMS: m/z calcd for C41H38N4 58Ni: 644.24480; found: 644.24500.
Compound 11: mp >350 ˚C, TLC: silica gel, CH2Cl2-PE (1:1): R f  = 0.58. ¹H NMR (360 MHz, C6D6): d = 1.97, 2.46 (2 s, 6 H, 3-CH3), 2.66, 2.82, 2.87, 2.95, 2.98, 2.99 (6 s, 18 H, 7-, 8-, 12-, 13-, 17-, 18-CH3), 6.48 (ddd, ³ J = 8.1 Hz, ³ J = 7.0 Hz, 4 J = 1.1 Hz, 1 H, aryl H), 7.03 (ddd, ³ J = 7.6 Hz, ³ J = 7.0 Hz, 4 J = 1.1 Hz, 1 H, aryl H), 7.25-7.32 (m, 2 H, aryl H), 7.59 (d, ³ J = 7.0 Hz, 1 H, aryl H), 7.68-7.70 (m, 1 H, aryl H), 7.79 (d, ³ J = 8.6 Hz, 1 H, aryl H), 8.45-8.47 (m, 1 H, aryl H), 8.02, 9.12, 9.16, 9.68 (4 s, 4 H, 5-, 10-, 15-, 20-H). UV/Vis (CHCl3): lmax (lg e) = 344 nm (4.618), 444 (4.680), 590 (4.123), 687 (4.683). MS (DCI, negative, NH3): m/z (%) = 646 (12), 645 (28), 644 (46), 643 (51), 642 (100) [M-]. HRMS: m/z calcd for C41H36N4 58Ni: 642.22937; found; 642.22907.