Skeletal Rearrangement of Twisted Thia‐Norhexaphyrin: Multiply Annulated Polypyrrolic Aromatic Macrocycles

Abstract

A hybrid thia‐norhexaphyrin comprising a directly linked N‐confused pyrrole and thiophene unit (1) revealed unique macrocycle transformations to afford multiply inner‐annulated aromatic macrocycles. Oxidation with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone triggered a cleavage of the C−S bond of the thiophene unit, accompanied with skeletal rearrangement to afford unique π‐conjugated products: a thiopyrrolo‐pentaphyrin embedded with a pyrrolo[1,2]isothiazole (2), a sulfur‐free pentaphyrin incorporating an indolizine moiety (3), and a thiopyranyltriphyrinoid containing a 2H‐thiopyran unit (4). Furthermore, 2 underwent desulfurization reactions to afford a fused pentaphyrin containing a pyrrolizine moiety (5) under mild conditions. Using expanded porphyrin scaffolds, oxidative thiophene cleavage and desulfurization of the hitherto unknown N‐confused core‐modified macrocycles would be a practical approach for developing unique polypyrrolic aromatic macrocycles.

Computational study of aromaticity, 1H NMR spectra and intermolecular interactions of twisted thia-norhexaphyrin and its multiply annulated polypyrrolic derivatives

“…One should stress that our GIMIC . 17 The GIMIC results are also in excellent agreement with the previously published NICS(0) local aromaticity indices for all studied porphyrinoids 1-5. 17…”

“…The ground electronic singlet state (S 0 ) structures of the studied porphyrinoids 1-5 have been optimized using the B3LYP/6-31G(d) [18][19][20] method at the DFT level starting from the initial molecular geometries obtained by the single-crystal X-ray diffraction technique. 17 Based on the optimized geometries QTAIM analysis 21 of the electronic density distribution functions has been carried out. The non-covalent interactions have been identified by the presence of (3, À1) type critical points and bond paths between the interacting atoms.…”

“…In contrast to compounds 1 and 4, porphyrinoids 2, 3 and 5 demonstrate clear global aromatic character and significant net diatropic ring currents (21.8, 22.1 and 28 nA T À1 , respectively) in agreement with the previously reported ACID and NICS calculations. 17 However, our GIMIC calculations make it possible to determine the multiple global aromatic pathways within each porphyrinoid molecule (2, 3 and 5) based on the absolute value of the current strength along the selected bond and quantitative splitting of this current at the bifurcation points (marked by turquoise spots in Fig. 3).…”

“…2 and 3) cannot be identified with the conjugation circuits usually presented for the porphyrinoid systems. 17,[39][40][41] The conjugation circuits are based on general chemical principles and single-crystal X-ray information about single/double bond alternation. Rather, the current pathways predicted by GIMIC demonstrate the real distribution of the magnetic currents due to the perturbation of the delocalized p-electronic molecular shell by the external magnetic field (usually applied perpendicular to the molecular plane).…”

“…In the present work we focus on the electronic structure and 1 H NMR spectra of five recently synthesized 17 unique porphyrinoids (Fig. 1) -core-modified norhexaphyrin (1) containing a thiophene ring and four products of its oxidation: thiopyrrolo-pentaphyrin with an embedded pyrrolo [1,2]isothiazole (2), a sulfur-free pentaphyrin incorporating an indolizine moiety (3), thiopyranyltriphyrinoid containing a 2H-thiopyran unit (4) and a fused pentaphyrin containing a pyrrolizine moiety (5) which is formed upon desulfurization reaction of compound (2).…”