Synthesis of Peripherally Nitrated, Aminated, and Arylaminated Subporphyrins

Abstract

2-Nitro-5,10,15-tri(4-tert-butylphenyl)subporphyrin 2 was prepared by the nitration of 5,10,15-tri(4-tert- butylphenyl)subporphyrin 1a with five equivalents of Cu(NO3)2·5H2O in a mixed EtOAc/Ac2O solution and was reduced into 2-amino-5,10,15-tri(4-tert-butylphenyl)subporphyrin 3. Bromination of 5,10,15-triphenylsubporphyrin 1b with 1.5 equivalents of N-bromosuccinimide (NBS) gave 2-bromo-5,10,15-triphenylsubporphyrin, which was converted into various 2-arylamino-5,10,15-triphenylsubporphyrins (4a-4d) and 2-benzamido-5,10,15-triphenylsubporphyrin 5 through Pd-catalyzed cross-coupling reactions. These molecules constitute the first examples of mono-β-substituted subporphyrins. These subporphyrins exhibit significantly perturbed optical and electrochemical properties, which reflect a large influence of the peripherally attached substituents on the electronic networks of subporphyrins.

meso‐Nitro‐ and meso‐Aminosubporphyrinatoboron(III)s and meso‐to‐meso Azosubporphyrinatoboron(III)s

“…Previously, meso ‐triphenylsubporphyrin B ‐methoxide was nitrated with Cu(NO 3 ) 2 to give a β‐nitrated compound in good yield. However nitration of meso ‐free subporphyrin 8 with Cu(NO 3 ) 2 gave an almost inseparable mixture of mono‐ and di‐nitrated subporphyrins . We found that nitration of 8 with AgNO 2 and I 2 in CH 2 Cl 2 /MeCN was slow but gave meso ‐nitrosubporphyrin 9 selectively in 71 % yield after stirring for 12 h at room temperature (Scheme ).…”

“…Reduction of 9 with NaBH 4 and Pd/C quantitatively gave meso ‐aminosubporphyrin 10 . Notably, 10 was obtained as fairly stable solid, while β‐aminosubporphyrin was reported to be unstable on silica gel . Finally, oxidation of 10 was attempted with PbO 2 .…”

“…[6] fairly stable solid, while b-aminosubporphyrin was reportedt o be unstable on silica gel. [7] Finally,oxidation of 10 was attempted with PbO 2 .W eh ad anticipated the oxidation of 10 might give meso-aminylr adical species 12 as an itrogen-congener of stable subporphyrin meso-oxyr adicals. [3d] However,t he reaction proceeded smoothly to give meso-to-meso azosubporphyrin 11 in 83 %y ield as as ingle product.…”

“…However nitration of meso-free subporphyrin 8 [3a] with Cu(NO 3 ) 2 gave an almost inseparable mixture of mono-andd initrated subporphyrins. [7] We found that nitration of 8 with AgNO 2 and I 2 in CH 2 Cl 2 /MeCN [6a] was slow but gave meso-nitrosubporphyrin 9 selectively in 71 %y ield after stirring for 12 h at room temperature (Scheme 2).Reduction of 9 with NaBH 4 and Pd/C quantitatively gave meso-aminosubporphyrin 10.N otably, 10 was obtaineda s Scheme1.meso-Heteroatom-appended subporphyrins 1-7.…”

Singly and Doubly Quinoxaline‐Fused BIII Subporphyrins

“…Taking advantage of this feature, many interesting examples have been explored. β‐Substituted subporphyrins have been also developed, such as β‐halogenated, β‐nitrated, β‐aminated, and β‐sulfanylated subporphyrins . But there are only limited examples of β‐π‐extended subporphyrins and only tribenzosubporphines 1 and meso ‐triphenyl‐tribenzosubporphyrins 2 were reported .…”