Porphyrins in 1,3-Dipolar Cycloaddition Reactions: Synthesis of a Novel Pyrazoline-fused Chlorin and a Pyrazole-fused Porphyrin

Abstract

β-Nitro-meso-tetraphenylporphyrin reacts with diazomethane to give a pyrazoline-fused chlorin as the main product. This compound was converted into the corresponding pyrazole-fused porphyrin, by treatment with DBU, and into a methanochlorin by refluxing in toluene.

cycloadditions - diazo compounds - porphyrins - chlorins - pyrazolines

References

1 Lash TD. J. Porphyrins Phthalocyanines  2001,  5:  267 

2 Kobayashi N. Konami H. J. Porphyrins Phthalocyanines  2001,  5:  233 

3 Lash TD. In The Porphyrin Handbook   Vol. 2:  Kadish KM. Smith KM. Guilard R. Academic Press; San Diego: 2000.  Chap. 10. p.125 

4 Tomé AC. Lacerda PSS. Neves MGPMS. Cavaleiro JAS. Chem. Commun.  1997,  1199 

5 Silva AMG. Tomé AC. Neves MGPMS. Cavaleiro JAS. Tetrahedron Lett.  2000,  41:  3065 

6 Alonso CMA. Neves MGPMS. Tomé AC. Silva AMS. Cavaleiro JAS. Tetrahedron Lett.  2001,  42:  8307 

7 Silva AMG. Tomé AC. Neves MGPMS. Silva AMS. Cavaleiro JAS. Chem. Commun.  1999,  1767 

8 Silva AMG. Tomé AC. Neves MGPMS. Silva AMS. Cavaleiro JAS. Perrone D. Dondoni A. Tetrahedron Lett.  2002,  43:  603 

9 Silva AMG. Faustino MAF. Tomé AC. Neves MGPMS. Silva AMS. Cavaleiro JAS. J. Chem. Soc., Perkin Trans. 1  2001,  2752 

10 β-Nitro-meso-tetraphenylporphyrin was obtained in 86% yield by nitration of TPP with Cu(NO₃)₂ in acetic anhydride, followed by acid treatment, according to the procedure described by: Giraudeau A. Callot HJ. Jordan J. Ezhar I. Gross M. J. Am. Chem. Soc.  1979,  101:  3857 

11 Callot HJ. Tetrahedron Lett.  1972,  1011 

12 Jaquinod L. Gros C. Olmstead MM. Antolovich M. Smith KM. Chem. Commun.  1996,  1475 

13 Jaquinod L. Gros C. Khoury RG. Smith KM. Chem. Commun.  1996,  2581 

14

Reaction of β-nitro-meso-tetraphenylporphyrin with diazomethane: a solution of 1 (50.6 mg, 0.08 mmol) in diethyl ether (200 mL) was saturated twice with diazomethane and allowed to stand at r.t. during 15 d. The reaction was monitored by TLC and UV/Vis spectra. Since after this period a significant quantity of porphyrin 1 remained, the reaction mixture was saturated again with diazomethane and left at r.t. for another period of 15 d. The solvent was then evaporated to dryness and the residue was purified by column chromatography in silica gel using a mixture of petroleum ether-dichloromethane (1:1) as eluent. The first fraction corresponded to a small amount of the methanochlorin 4 (1.7 mg, 3%) and the second one to the unchanged starting porphyrin 1 (23.0 mg, 45%). The third fraction was the pyrazoline-fused chlorin 2 (22.2 mg, 41%), which was followed by a small amount of the pyrazole-fused porphyrin 3 (3.3 mg, 7%).

15

Spectroscopic data for chlorin 2: ¹H NMR (300 MHz, CDCl₃, J in Hz): δ = -2.15 and -2.12 (2 s, 2 H, NH); 4.75 (dd, 1 H, J = 19.0 and J = 4.7, H-2^{3 trans} ); 5.08 (dd, 1 H, J = 19.0 and J = 9.2, H-2^{3 cis} ); 5.45 (dd, 1 H, J = 9.2 and J = 4.7, H-3); 7.56-7.62, 7.70-7.78, 7.87-7.90 and 7.99-8.24 (4 m, 20 H, H-Ph); 8.29 and 8.38 (2 dd, 2 H, J = 4.9 and J = 1.8, H-β); 8.51 and 8.54 (2 d, 2 H, J = 4.9, H-12,13); 8.67 and 8.72 (2 dd, 2 H, J = 4.9 and J = 1.8, H-β). MS (LSIMS): 702 [M + H]⁺, 674 [(M - N₂) + H]⁺, 655 [(M - HNO₂) + H]⁺, 627 {[(M - HNO₂) - N₂] + H}⁺. UV/Vis (CH₂Cl₂): λ_max/nm (log ε): 639 (4.47), 588 (3.98), 546 (4.29), 516 (4.24), 410 (5.39). Anal. Calcd for C₄₅H₃₁N₇O₂.H₂O: C, 75.09; H, 4.62; N, 13.62. Found: C, 74.86; H, 4.19; N, 14.10.

16

Spectroscopic data for porphyrin 3: ¹H NMR (300 MHz, CDCl₃, J in Hz): δ = -2.86 (s, 2 H, NH); 7.04 (s, 1 H, H-2³); 7.73-7.91 (m, 12 H, H _meta+para -Ph); 8.17-8.22 (m, 8 H, H _ortho -Ph); 8.75 (s, 2 H, H-12,13); 8.84-8.96 (m, 4 H, H-β). UV/Vis (CH₂Cl₂): λ_max/nm (log ε): 639 (3.18), 585 (3.90), 546 (3.88), 513 (4.34), 417 (5.67). MS (LSIMS): 655 [M + H]⁺, 654 [M⁺]. MS-HRFAB exact mass m/z for C₄₅H₃₀N₆ [M + H]⁺: calcd 655.2610, found 655.2628.

17

Spectroscopic data for methanochlorin 4: ¹H NMR (300 MHz, CDCl₃, J in Hz): δ = -2.08 (s, 2 H, NH), 1.95 (dd, 1 H, J = 5.4 and J = 5.2, H-2^{1 trans} ); 3.36 (dd, 1 H, J = 10.0 and J = 5.2, H-2^{1 cis} ); 4.59 (dd, 1 H, J = 10.0 and J = 5.4, H-3); 7.61-7.78 (m, 12 H, H _meta+para -Ph); 7.98-8.23 (m, 8 H, H _ortho -Ph); 8.46 (dd, 1 H, J = 4.9 and J = 1.5, H-β), 8.52 (s, 2 H, H-12,13); 8.56 (dd, 1 H, J = 4.9 and J = 1.5, H-β), 8.70-8.73 (m, 2 H, H-β); UV/Vis (CH₂Cl₂): λ_max/nm (rel. int.): 646 (12%), 592 (7%), 548 (10%), 519 (11%), 415 (100%). MS (LSIMS): 674 [M + H]⁺, 673 [M⁺]. MS-HRFAB exact mass m/z for C₄₅H₃₁N₅O₂ [M + H]⁺: calcd 674.2556, found 674.2542.