Azulichlorins and Benzocarbachlorins Derived Therefrom

Abstract

Acid-catalyzed condensation of azulidipyrrane aldehydes with a dihydrodipyrrin carbaldehyde afforded the first examples of azulichlorins. These macrocyclic products were isolated in a monoprotonated form, and the free bases proved to be somewhat unstable. The monocations were strongly diatropic, and proton NMR spectroscopy showed the internal C−H at ca. −2 ppm. Addition of TFA gave the related dications, but these exhibited significantly reduced aromatic ring currents. Reaction of an azulichlorin with tert-butyl hydroperoxide and KOH in dichloromethane/methanol gave a benzocarbachlorin and two related aldehydes. The UV−vis spectrum for the benzocarbachlorin showed a split Soret band at 414 and 430 nm, together with a strong chlorinlike absorption at 684 nm. The proton NMR spectrum indicated that the carbachlorin is strongly aromatic and the internal C− H was observed at −4.64 ppm. Addition of TFA afforded a C-protonated dication with a significantly increased diatropic ring current. The proton NMR spectrum, NICS calculations, and AICD plots indicated that the system favors a 22π electron delocalization pathway that runs through the fused benzo unit. Addition of TFA to the benzocarbachlorin aldehydes primarily led to the formation of monocations, and the generation of C-protonated dications was no longer favored due to the presence of electron-withdrawing formyl moieties.

Telluracarbaporphyrins and a Related Palladium(II) Complex: Evidence for Hypervalent Interactions

“…The aromatic characters of heterocarbaporphyrins were assessed using nuclear independent chemical shift (NICS) calculations and anisotropy of induced current density (AICD) plots, methods we have previously applied to related porphyrinoid systems. − NICS(0) calculations are commonly used to identify the aromatic characteristics of porphyrinoid systems, but the results can be misleading, as the effects of both the σ and π electrons are included. NICS zz calculations carried out 1 Å above the ring (NICS(1) zz ) emphasize contributions from the π system, and this method is a more reliable indicator of macrocyclic diatropicity.…”

Synthesis, Structure, Spectral, and Anion Sensing Studies of an Aromatic meso-Fused Boron(III) Benzitriphyrin(2.1.1) Complex

“…The type i and j protons of the benzene ring are shifted downfield since they are a part of the global aromatic circuit, and the resonance values are comparable to those of an aromatic carbatriphyrin complex. 31,32 All of the proton resonances in compound 10 were shifted downfield in comparison to its phlorin analogue 7, supporting the presence of a diatropic ring current and also validating the aromatic nature of the B(III) complex of benzitriphyrin(2.1.1). Complex 10 showed a broad resonance at −2.56 ppm in 11 B NMR (Figure S5 in the Supporting Information).…”

Synthesis of Azulitriphyrins(1.2.1) and Related Benzocarbatriphyrins

“…It has been suggested that these transformations involve initial nucleophilic attack onto the azulene rings and that this triggers a Cope rearrangement, which leads to the observed benzocarbaporphyrins. Azulichlorins were recently shown to undergo similar ring contractions, providing access to a new class of benzocarbachlorins . It was much less clear that azulitriphyrins(1.2.1) would undergo transformations of this type as nucleophilic additions to this system appeared to give complex results.…”

“…Furthermore, the seven-membered ring is prone to nucleophilic attack and this facilitates oxidative ring contractions with peroxides under basic conditions to afford benzocarbaporphyrins 2 . The intriguing properties of azuliporphyrins have led to the preparation of other azulene-containing porphyrinoids, including azulisapphyrin 3 , azulicorrole 4 , azulichlorins 5 , dioxa-, dithia-, diselena- and ditellura-diazuliporphyrins, adj -diazuliporphyrins 6 , and related conjugated systems (Figure ). Although expanded azuliporphyrins have been investigated, the only example of a contracted azuliporphyrinoid is azulicorrole 4 .…”