2-(Naphthalen-1-yl)thiophene as a New Motif for Porphyrinoids: Meso-Fused Carbaporphyrin

Abstract

The first synthesis of meso-fused carbaporphyrin via a premodification method was accomplished by substituting two pyrrole moieties and one meso-carbon with 2-(naphthalen-1-yl)thiophene. The obtained global π-conjugation pathway of the macrocycle noticeably disturbs the 10π local aromaticity of naphthalene, and its aromatic nature was supported by NMR spectroscopy together with nucleus-independent chemical shift, anisotropy of the induced current density, and harmonic oscillator stabilization energy calculations. In addition, the meso-fused carbaporphyrin also allowed the formation of a square planar Pd(II) complex.

Polycyclic Aromatic Hydrocarbon‐/Heterocycle‐Embedded Porphyrinoids

“…Cho and co-workers reported the synthesis of fused thia-1,7naphthiporphyrins 16 a-b as shown in Scheme 3. [10] The precursor, 5-(7-formylnaphthalen-1-yl)thiophene-2-carbaldehyde 19 was prepared by Suzuki coupling reaction of 8-iodo-2naphthaldehyde 17 with (5-formylthiophen-2-yl)boronic acid 18 in the presence of Pd(0) catalyst in DMF/H 2 O in 83% yield. The 1-thienylnaphthalenediols 20 a-b were synthesized by treating 19 with appropriate aryl bromides under Grignard reaction conditions in 55-65% yields.…”

“…Cho and co‐workers reported the synthesis of fused thia‐1,7‐naphthiporphyrins 16 a – b as shown in Scheme . The precursor, 5‐(7‐formylnaphthalen‐1‐yl)thiophene‐2‐carbaldehyde 19 was prepared by Suzuki coupling reaction of 8‐iodo‐2‐naphthaldehyde 17 with (5‐formylthiophen‐2‐yl)boronic acid 18 in the presence of Pd(0) catalyst in DMF/H 2 O in 83% yield.…”

Synthesis of a Phlorin from a Meso‐Fused Anthriporphyrin by a Diels–Alder Strategy

“…These results indicate that the anthracene in macrocycle 4 still has the largest number of p-sextets but the local aromaticity of anthracene is disturbed. Them aximum difference between the chemical shifts of the peripheral CH moieties and those of the interior CH or NH moieties is generally considered to be ab enchmark for aromaticity.M ore specifically,the values of Dd CH-CH = 4.6 ppm (anthracene) and Dd CH-NH = 3.3 ppm are slightly lower than those of the weakly aromatic p-benziporphyrin (i.e., Dd CH-CH = 5.35 ppm at 168 K) [19] and the meso-fused naphthiporphyrin (3, Dd CH-CH = 5.7 ppm (naphthalene) and Dd CH-NH = 5.1 ppm), [11] thus indicating the presence of aw eak diatropic ring current in 4. Thus,t he chemical shifts of all peripheral b-CH groups and anthracene CH moieties are shifted downfield as compared to the equivalent signals of diol 10 ( Figure 3a).…”

“…However, phlorins have their own merits.F or example,phlorin derivatives are important intermediates for the synthesis of skeletally modified porphyrins. [11] Thecharacteristics of the porphyrinoid revealed that the global aromaticity of the macrocycle disrupted the 10p local aromaticity of the naphthalene unit. [5] Synthetically,unmodified phlorins are prepared by either reducing one meso-carbon atom of porphyrinoids with nucleophiles,s uch as hydride [6] and lithium reagents, [7] or condensing dipyrromethanecarbinol and dipyrromethane equivalents.…”

“…[10] Recently,t ogether with the Furuta research group,w e reported the first example of ameso-fused carbaporphyrin 3 ( Figure 1). [11] Thecharacteristics of the porphyrinoid revealed that the global aromaticity of the macrocycle disrupted the 10p local aromaticity of the naphthalene unit. Thus,w e wondered if ameso-fused carbaporphyrin could be expanded by replacing the contained arene and used as an intermediate for porphyrinoid synthesis.S pecifically,a nthracene was selected to examine the expandability of the system.…”