Pyreniporphyrins: Porphyrin Analogues That Incorporate a Polycyclic Aromatic Hydrocarbon Subunit within the Macrocyclic Framework

Abstract

The first examples of porphyrin analogues incorporating pyrene units are reported. Acid-catalyzed condensation of a pyrene dialdehyde with a tripyrrane, followed by oxidation with DDQ, afforded a polycyclic aromatic hydrocarbon (PAH)-porphyrin hybrid in 38% yield. Pyreniporphyrin proved to be devoid of global aromatic character, but upon protonation aromatic mono- and dicationic species were generated. In the proton NMR spectrum for the dication, the internal CH was shifted upfield to approximately +3 ppm. NICS calculations and ACID plots confirmed the diatropic nature of these structures. Pyreniporphyrin reacted with palladium(II) acetate to give excellent yields of a palladium(II) complex that showed weakly diatropic properties. Treatment of the pyrene dialdehyde with phenylmagnesium bromide generated a dicarbinol that reacted with excess pyrrole in the presence of boron trifluoride etherate to give a tripyrrane analogue. Lewis acid catalyzed ring closure with a thiophene dialcohol in 2% ethanol-dichloromethane afforded a tetraphenylthiapyreniporphyrin in 31% yield. This porphyrinoid was nonaromatic in the free-base form but showed significant diatropicity upon protonation. These results demonstrate that PAH-porphyrin hybrids are easily accessible, and this strategy may allow the incorporation of even larger aromatic subunits.

Helicenophyrins: Expanded Carbaporphyrins Incorporating Aza[5]helicene and Heptacyclic S‐Shaped Aza[5]helicene Motifs

“…The 1 HNMR spectrum of 7 H2 is consistent with a C 1 -symmetric structure containing three pyrrole rings and the aza [5]helicene motif ( Figure 2). In addition, five protons of the aza [5]helicene gave rise to AMX (H2, H3, H32) and AX (H8, H9) spin systems.T wo broad signals at d = 11.21 and 10.92 ppm correspond to NH39 and NH37 of pyrroles Fand H, respectively.T heir downfield positions,i n comparison to nonaromatic meso-anthriporphyrin, [3] reflect the formation of internal hydrogen bonds within the F-G-H loop.T he nonaromaticity of 7 H2 was corroborated by the appearance of the b-pyrrolic AB patterns in the d = 6.30-7.30 ppm range typical for nonaromatic porphyrinoids.…”

“…[9] In spite of the impressive exploration of the chemistry of expanded porphyrins,s tudies on expanded carbaporphyrinoids remain rather limited. [12][13][14][15] Significantly,o xidative ring fusion reactions,t ransforming ortho-phenylene-bridged hexapyrroles and hexathiophenes into helicenophanes incorporating pentaaza [9]helicene and hexathia [9]/ [5]helicene moieties,respectively,have been recently described by Osuka and co-workers. This formal expansion leads to the phenanthriporphyrinoids 2 NH and 3 as outlined at Scheme 1.…”

“…Abstract: Incorporation of phenanthrene into ah exaphyrin(1.1.1.1.1.0) frame resulted in intramolecular ring fusion, thus giving rise to chiral helicenophyrins.T hese molecules contain helicene and porphyrin features by incorporating either an aza [5]helicene or heptacyclic S-shaped aza [5]helicene.…”

“…[1,2,11] In the pursuit of expanded carbaporphyrinoids,a na pproach involving as ystematic, gradual incorporation of (E)-2-benzylidene-2H-pyrrole unit-(s) into the parent 1 is being explored. [15] Herein we report on the synthesis,reactivity,and characterization of the constitutional isomer of 3, the chiral helicenophyrin 7 H2 incorporating an unprecedented aza- [5]helicene motif (Scheme 2). In principle,t his strategy has been recently exemplified by formation of the heterophenanthrisapphyrins 2 X .…”

“…This formal expansion leads to the phenanthriporphyrinoids 2 NH and 3 as outlined at Scheme 1. Thes ubsequent ring fusion afforded ab idirectional, heptacyclic S-shaped aza [5]helicene unit as depicted in 8 H (for structure see Scheme 3). [4] Accordingly,t he dimethoxyphenanthrihexaphyrin(1.1.1.1.1.0) 3 and its reduced form 4 have been set as rational synthetic targets.I nt he process we realized that geometric constraints of 4 enforced intramolecular ring fusion leading to anovel macrocycle,thereby interweaving features of helicenes and porphyrins.Inlight of their architecture,itis essential to recall that rare examples of the perimeter attachment of helicenes to porphyrin or phthalocyanine motifs have been reported.…”