Regioselective Internal Carbonylation of the 2-Aza-21-carbaporphyrin: Access to Configurationally Stable Chiral Porphyrinoids

Abstract

Reaction of paraformaldehyde with meso-tetraaryl-2-aza-21-carbaporphyrins (NCP) in the presence of a basic catalyst afforded fused lactam derivatives comprising a >C═O bridge linking the internal carbon C21 with one of the internal nitrogens. The isomer 2 with C21-C(O)-N24 bridge is formed with about 9-fold molar excess over that with C21-C(O)-N22 bridge (3). The (1)H NMR and UV-vis spectral characteristics indicate aromatic character of the derivatives. For meso-tetrakis(3',5'-dimethoxy)- and meso-tetrakis(3',4',5'-trimethoxy)-21,24-carbonyl-NCP an efficient external ring fusion by linking C3, i.e., the external carbon of the confused pyrrole, with an ortho carbon of the adjacent aryl was observed under acidic conditions, yielding derivatives 4c and 4d, comprising a linear system of five fused rings. The chirality and configurational stability of these carbonylated systems were established by a chiral stationary phase HPLC and circular dichroism. The interaction of 2 with chiral acids and alcohols leading to the formation of diastereomers was observed by (1)H NMR. Slow racemization of 2 under acidic conditions was established by HPLC and (1)H NMR and a mechanism for this process was proposed.

Core chemistry and skeletal rearrangements of porphyrinoids and metalloporphyrinoids

“…Several reactions affording inner-core bridged N-confused porphyrin have been reported, although the nature of the linker differs distinctively in each case. N-confused porphyrin 1b reacts with formaldehyde producing the two internally carbonylated products 115 and Scheme 45) 136. A strong preference was observed in favor of 115 as the molar ratio, established on the basis of the 1 H NMR spectra, amounting to 10:1.Scheme 45.…”

Bis(N‐Confused Porphyrin) as a Semirigid Receptor with a Chirality Memory: A Two‐Way Host Enantiomerization through Point‐to‐Axial Chirality Transfer

“…A case of diastereoselective interaction with CSAH, other chiral acids, and alcohols has been recently described for a monomeric internally carbonylated NCP derivative that is intrinsically chiral. [68] A low-temperature 1 H NMR titration (CDCl 3 , 213 K) of 2 with enantiopure S-CSAH allows the observation of diastereomers for mono-and dications under slow-exchange conditions. A difference in the diastereomer populations of [2-H 2 ](S-CSA) 2 increases with the concentration of acid ( Figure 4) up to a diastereomeric excess of more than 40 % (de = j n MS Àn PS j /(n MS + n PS )), although the dication is not the most abundant species throughout the titration.…”

“…Upon the addition of the racemic acid to racemic 2 , tetracation [ 2 ‐H 4 ] 4+ of a given configuration discriminates between the R and S anions and forms a complex with the ion that matches the binding sites better. A case of diastereoselective interaction with CSAH, other chiral acids, and alcohols has been recently described for a monomeric internally carbonylated NCP derivative that is intrinsically chiral 68…”

Synthesis of 2-Cyano-3-Nitroporphyrin Derivatives with Silyl Cyanide

“…11 Trimethylsilyl cyanide (TMSCN) is a better source of cyanide than the alkali metal cyanides, being readily available, easy to handle and possessing high activity. 12 In continuation of our previous work on the synthesis of porphyrinoid derivatives, [13][14][15][16][17][18][19][20] in this paper we report the synthesis of 2-cyano-3-nitroporphyrin derivatives by the reaction of 2-nitroporphyrin with TMSCN in the presence of tetrabutylammonium fluoride (TBAF) in tetrahydrofuran (THF) at room temperature (Scheme 1).…”