Cyclo[8]isoindoles: Ring‐Expanded and Annelated Porphyrinoids

Abstract

Cyclo[8]isoindol, das über eine sattelförmige Struktur verfügt (siehe Bild, 2), wurde durch oxidative Kupplung von Bicyclo[2.2.2]octadien(BCOD)‐kondensierten 2,2′‐Bipyrrolen und anschließende Retro‐Diels‐Alder‐Reaktion eines BCOD‐kondensierten Cyclo[8]pyrrols (1) synthetisiert. Schlüsseltrends bei den optischen Spektren ringanellierter Cyclo[8]pyrrole werden anhand von magnetischen Circulardichroismus‐Spektren und theoretischen Rechnungen beschrieben.

Acenaphthylene‐Fused Cyclo[8]pyrroles with Intense Near‐IR‐Region Absorption Bands

“…An intense band is observed in the spectrum of 1 a in the near‐IR region at λ =1482 nm, while there is a weaker band in the visible region at λ =512 nm. The spectra are similar to those reported for the parent cyclo[8]pyrrole1 and the bicyclo[2.2.2]octadiene (BCOD)‐fused cyclo[8]pyrrole, which we have reported previously3 (Figure 4), but the major spectral bands are shifted significantly to the red. The relative intensities of the major spectral bands in the near‐IR and visible regions differ markedly from those observed in the electronic‐absorption spectrum of cyclo[8]isoindole ( 2 ), which contains fused‐benzene rather acenaphthylene moieties, but is similar to that observed in the spectra of cyclo[8]pyrroles 1.…”

“…Attempts were made to increase the yield by modifying the reaction conditions. Ce(SO 4 ) 2 was used as an oxidant with H 2 SO 4 , Na 2 SO 4 , and TBAHSO 4 (TBA=N( n Bu) 4 ) in a manner similar to the approach described in our previous report on cyclo[8]isoindole3 to afford 1 a and 1 b ( R f =0.6 and 0.9, respectively) in 33 and 7 % yields, respectively (Table 1, entry 2). Cyclo[8]pyrroles 1 a and 1 b were obtained in moderate yields in the absence of Na 2 SO 4 and H 2 SO 4 (Table 1, entries 3 and 4).…”

“…To date, there have been only two examples. Recently, we reported the first example of a π‐expanded cyclo[8]pyrrole, namely cyclo[8]isoindole (Figure 1), which has a slightly red‐shifted absorption band at λ =1078 nm 3. Sessler and Panda subsequently reported a cyclo[4]naphthobipyrrole compound that has a red‐shifted near‐IR absorption band which lies beyond λ =1200 nm 4.…”

Cyclo[4]naphthobipyrroles: Naphthobipyrrole‐Derived Cyclo[8]pyrroles with Strong Near‐Infrared Absorptions

“…During the preparation of this manuscript, cyclo [8]iso- [18] Therefore, we explored their optimal reaction conditions for our synthetic purpose and compared the properties of the 2 and 3 with our cyclo[4]naphthobipyrroles. The precursors, b-dialkylnaphthobipyrroles, reported recently by us and Sesslers group independently, were synthesised following our strategy.…”

“…Further, use of the optimised condition of Okujima et al, that is, cerium sulfate in presence of 6 m sulphuric acid and sodium sulfate and tetraA C H T U N G T R E N N U N G (n-butyl)ammonium bisulfate as additives [18] did not lead to the formation of 5 a (even by extending the reaction time from 2 to 5 days, entry 4), wheras 5 b could be obtained in much lower yield (3 % after 2 days and did not increase further even after 5 days, entry 8).…”