Multipyrrolic Macrocycles DOI: 10.1002/ange.201007510 Cyclo[8]isoindoles: Ring-Expanded and Annelated Porphyrinoids** Tetsuo Okujima,* Guangnan Jin, Naoki Matsumoto, John Mack, Shigeki Mori, Keishi Ohara, Daiki Kuzuhara, Chie Ando, Noboru Ono, Hiroko Yamada, Hidemitsu Uno, and Nagao Kobayashi* In recent years there has been a growing focus on the chemistry of ring-expanded porphyrins such as hexaphyrins and octaphyrins, because their properties differ markedly from those of conventional porphyrins in a manner that makes them potentially suitable for a number of novel practical applications. [1–5] Cyclo[8]pyrrole ([30]octa- phyrin(0.0.0.0.0.0.0.0)), along with its smaller cyclo[6]- and cyclo[7]pyrrole analogues, was first reported by Sessler and co-workers based on an oxidative coupling of 2,2’-bipyrrole with FeCl 3 . [6] A key structural difference with respect to the porphyrins is the complete absence of meso carbon atoms. [7] The photophysical, [5] anion-binding, [7a,b] and liquid-crystalline properties [7c] of cyclo[n]pyrroles (n = 6–8) have been studied in-depth, along with their electronic structures. [7d, 8] The UV/ Vis absorption spectra of cyclo[8]pyrroles contain a weaker band at approximately 430 nm (e  1  10 5 m 1 cm 1 ) and a more intense band at approximately 1100 nm (e  2 10 5 m 1 cm 1 ). [6a] The strong absorbance in the near-IR (NIR) region makes these compounds potentially suitable for use in optical storage and signaling devices. Despite the large variety of ring-annelated porphyrins that have been successfully synthesized, [9] there have been no reports of fused-ring-expanded cyclo[n]pyrroles, because the prepara- tion of the required precursors is extremely challenging. To date, only b-alkyl substituted compounds have been pre- pared. [6, 7] The ability to fine-tune the wavelengths of the major absorption bands based on structural modifications such as ring annelation would greatly enhance the utility of these compounds for practical applications. Herein, we report the first successful synthesis of cyclo[8]isoindole (3) based on an oxidative coupling of bicyclo[2.2.2]octadiene(BCOD)- fused 2,2’-bipyrrole (1), followed by the retro-Diels–Alder reaction of cyclo[8]BCODpyrrole (2 ; Scheme 1). We also report an in-depth analysis of the optical properties and electronic structures of 2 and 3 based on magnetic circular dichroism (MCD) spectroscopy and time-dependent (TD) DFT calculations. Recently, we reported the synthesis of benzosapphyrins using the retro-Diels–Alder strategy to form fused-ring- expanded porphyrins from precursors with fused BCOD groups. [10] A similar strategy is adopted to synthesize cyclo[8]- isoindoles. The BCOD-fused 2,2’-bipyrrole 1 was prepared from BCOD-fused pyrrole according to literature procedur- es. [10a, 11] Details of the synthesis of 2 under different con- ditions are summarized in Table 1. Initially, reaction con- ditions similar to those reported by Sessler and co-workers [6a] were adopted with a 1m H 2 SO 4 solution of FeCl 3 as the oxidant. In the procedure reported by Sessler and co-workers, the solution of 1 was slowly added to a mixture of the oxidant and acid over a period of 9 h by syringe pump. In contrast, we immediately added all of the FeCl 3 ·6H 2 O oxidant and H 2 SO 4 to a 2 mm solution of 1 in CHCl 3 and stirred the mixture for 45 minutes at 0 8C. After purification by silica gel column chromatography and gel permeation chromatography (GPC), 2 was obtained as deep blue crystals in 43 % yield. The MALDI-TOF mass spectrum contained a molecular ion peak Scheme 1. Structures of bipyrrole 1 and octaphyrins 2 and 3. [*] Prof. Dr. T. Okujima, Dr. G. Jin, N. Matsumoto, Prof. Dr. K. Ohara, D. Kuzuhara, C. Ando, Prof. Dr. N. Ono, Prof. Dr. H. Yamada, Prof. Dr. H. Uno Department of Chemistry and Biology Graduate School of Science and Engineering Ehime University, Matsuyama 790-8577 (Japan) Fax: (+ 81) 089-927-9615 E-mail: okujima.tetsuo.mu@ehime-u.ac.jp Homepage: http://chem.sci.ehime-u.ac.jp/ Dr. S. Mori Department of Molecular Science, Integrated Center for Sciences Ehime University, Matsuyama 790-8577 (Japan) Dr. J. Mack, Prof. Dr. N. Kobayashi Department of Chemistry, Graduate School of Science Tohoku University, Sendai 980-8578 (Japan) Fax: (+ 81)-022-795-7719 E-mail: nagaok@m.tohoku.ac.jp [**] This work was partially supported by Grants-in-Aid for the Scientific Researches on Innovative Areas (Nos. 21108517 and 20108007, p-Space to H.U. and N.K.), B (No. 22350083 to H.Y.), and C (No. 20550047 to H.U.) from the Japanese Ministry of Education, Culture, Sports, Science and Technology. We thank Venture Busi- ness Laboratory, Ehime University, for assistance in obtaining the MALDI-TOF mass spectra. We acknowledge the Nippon Synthetic Chem. Ind. (Osaka, Japan) for a gift of ethyl isocyanoacetate, which was used for the preparation of the starting pyrroles. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201007510. Angewandte Chemie 5817 Angew. Chem. 2011, 123, 5817 –5821  2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim