Notes Bull. Korean Chem. Soc. 2004, Vol. 25, No. 9 1421 Synthesis of Regioselectively Diiodinated Porphyrins; 5,20-Diaryl-12,13-diiodoporphyrins Pradeepta K. Panda, Sasmita Padhy, Kwon-Soo Ha, † and Chang-Hee Lee * Department of Chemistry, Kangwon National University, Chun-Chon 200-701, Korea † Department of Molecular & Cellular Biochemistry, Kangwon National University School of Medicine, Chun-Chon 200-701, Korea Received June 7, 2004 Key Words : Diiodinated porphyrins, 3,4-Diiodo-2,5-bis(hydroxymethyl)pyrrole, ‘3+1’ condensation Over the past decade there has been a significant number of reports on the synthesis and physico-chemical properties of a wide variety of halogenated porphyrins. Their unique physico-chemical properties 1 are partly attributed to the nonplanarity of the macrocycle mainly induced by the repulsive interactions among the peripheral substituents. Especially the high-valent metalloporphyrins are of great use as catalysts in many organic transformations. 2 Their catalytic activities are sensitive to the peripheral substituents and introduction of halogens has been known to be crucial for enhanced selectivity and activities. The electron-deficient porphyrins are generally resistant to oxidation and accord- ingly affect redox potentials. Synthesis of perhalogenated porphyrins are well established and most of the reports so far mainly dealt with bromo-, chloro- and fluoro- substituted porphyrins. 3 Much less is known about their iodo counter- parts on the other hand. Especially, availability of porphyrins bearing iodo-substitution in regioselective manner at β- pyrrolic positions has been limited. Introduction of two iodo groups at one of four pyrrolic β-positions would be more challenging when the porphyrin bears couple of different meso-substituents. The synthesis of β-iodo substituted porphyrins carrying multiple iodo groups has been reported in the case of duteroporphyrin IX dimethyl ester. 4 To the best of our knowledge on the other hand, there is no report on β- substitution of simple synthetic porphyrins with iodine. Herein, we report a simple ‘3 + 1’ condensation route for the synthesis of diiodoporphyrin derivatives utilizing substituted 3,4-diiodopyrrole with tripyrromethanes. The condensation resulted in the formation of diiodoporphyrins 1a and 1b bearing idodo groups at regioselectively designated positions. The key component in the synthesis of target porphyrin is 3,4-diiodo-2,5-bis(hydroxymethyl)pyrrole 3, which was synthesized by treating freshly prepared aqueous solution of KI 3 (1.0 M) with a methanolic solution of 2,5-bis(hydroxy- methyl)pyrrole 5 2. Immediately the color changed to light pink and the desired product precipitated as light pink flaky solids upon addition of excess water in 60% yield. The compound is quite stable at room temperature and can be stored in freezer for long time but undergoes degradation on heating with liberation of iodine. The identity of diol 3 was easily confirmed by observing disapperance of β-pyrrolic protons in 1 H NMR spectra. Condensation of 3 with simple unsubstituted tripyrro- methanes 6 4a in the presence of catalytic amount of BF 3 ·O(Et) 2 in acetonitrile followed by DDQ oxidation led to the formation of 2,3-diiodoporphyrin 1a, albeit in very low yield (< 1%). However use of 5,10-ditolyltripyrromethane 4b in same condensation process resulted in the formation of the corresponding porphyrin 1b upto 5%. The absorption data of 1a (Table 1) showed bathochromic shift of the soret band compared to those of porphine 7 (1c), while similar trend is observed for the Q-IV and Q-III transitions of the visible part. The spectral pattern of the Q- bands changed from the phyllo-type (1c) to etio-type (1a) Scheme 1 Table 1. UV/VIS absorption data of porphine, 2,3-diiodoporphyrin (1a) and 2,3-diiodo-10,15-ditolylporphyrin (1b) in benzene Comp Soret Q-IV Q-III Q-II Q-I 1c 395 (261000) 490 (16000) 520 (3000) 569 (4400) 616 (890) 1a 404 (91400) 499 (6470) 534 (4600) 569 (3060) 1b 419 (210800) 511 (14500) 545 (3200) 584 (4600) 639 (1520)