Synthesis of Azulitriphyrins(1.2.1) and Related Benzocarbatriphyrins

Abstract

Bis(pyrrolylmethyl)azulene dialdehydes underwent intramolecularMcMurry coupling, and following oxidation with DDQ and addition of trifluoroacetic acid, gave aromatic azulitriphyrin cations. The proton NMR spectra for these contracted carbaporphyrinoids showed the internal CH upfield at ca. 2 ppm, while the bridging methine units appeared downfield between 8 and 10 ppm, demonstrating that the macrocycles possess significant 14π electron diamagnetic ring currents. Although protonated azulitriphyrins(1.2.1) proved to be very stable, the free base forms were unstable and could not be isolated. Treatment of an azulitriphyrin with KOt-Bu-t-BuOOH gave rise to oxidative ring contractions that afforded the first examples of benzocarbatriphyrins. These contracted porphyrinoids also exhibit aromatic ring currents, and the internal CH resonances shifted upfield to 0.5−0.7 ppm. Protonation afforded cations with slightly enhanced diatropic properties. Nucleus independent chemical shift and anisotropy of induced current density calculations confirmed that benzocarbatriphyrins are 14π electron delocalized aromatic systems that bypass the fused arene units.

Recent advances in subphthalocyanines and related subporphyrinoids

“…Triphyrin analogues comprise a variety of macrocycles in which one or more pyrrole units of the triphyrin structure have been replaced by carbocycles, like in carbatriphyrins(3.1.1), 690 carbatriphyrins(2.1.1) ( 726 Fig. 126), 691 azulitriphyrins(1.2.1) ( 727 ), 692,693 or other types of carbatriphyrins, 694 including the triphyrin(2.1.1)-tetraphyrin(1.1.1.1) hybrid 737 . 695 Substitution of one pyrrole ring by other heterocycles also produces triphyrin analogues.…”

Porphyrinoids with Vinylene Bridges

“…In addition, [14]azulitriphyrin(2.1.1) 22a can be transformed into benzocarbatriphyrin(2.1.1) 23a, which shows porphyrin-like aromatic properties. 39 Ortho-phenylene and thiophene-fused oxatriphyrins(2.1.1) 25 were reported by Latos-Grażyński and co-…”

“…In addition, [14]azulitriphyrin(2.1.1) 22a can be transformed into benzocarbatriphyrin(2.1.1) 23a, which shows porphyrin-like aromatic properties. 39 Ortho-phenylene and thiophene-fused oxatriphyrins(2.1.1) 25 were reported by Latos-Grażyński and co- 37 The Ravikanth group prepared the nonsymmetric benzene-fused oxatriphyrin(2.1.1) 28a and thiatriphyrin(2.1.1) 28b in four steps starting from 1-benzofuran and 1-benzothiophene, respectively (Scheme 11). 42 The nonaromatic dibenzofuran/dibenzothiophene-based triphyrins(2.2.1) 30a and 30b, and their Re(I) complex were also reported by the same group (Scheme 10).…”

“…The thiophene ring is tilted and two pyrroles form a nearly planar structure because steric hindrance between the lone pairs is canceled out and a hydrogen bond forms between the pyrroles as a result of protonation of a pyrrole ( Figure 2). [14]Oxatriphyrin(2.1.1) 19 37 and [14]azulitriphyrin(2.1.1) 22 38,39 were also obtained as their protonated forms for the same reason as 16. The angle of tilt of the furan in 19a is smaller than that of 16, reflecting the atomic radii ( Figure 2).…”

Development of Heterocycle-Substituted and Fused Azulenes in the Last Decade (2010–2020)

“…Okujima et al [ 97 ] and Lash et al [ 98 ] subsequently reported azulitriphyrin with triphyrin(2.1.1) framework. Intramolecular McMurry coupling of diformyltripyrrane is a key step for the construction of the triphyrin(2.1.1) framework ( Scheme 62 ) [ 99 ].…”