A selective electrophilic nitration of meso-tetraarylporphyrin copper(II) and nickel(II) complexes, bearing in meso-aryl rings a variety of substituents (3- NO 2, 3- CH 3, 3- Cl , 2,3,4,5,6-pentafluoro-, and 2,6-dichloro-), is described. The reactions of the above porphyrinates, carried out in CHCl 3 at room temperature, with aqueous HNO 3 (concentration 15-50%), resulted in the formation of the respective mono-β-nitrated products, in good or very good yield (74-93%). All the synthesized compounds were demetallated in CF 3 CO 2 H/H 2 SO 4 mixture to give β-nitro-substituted porphyrin free bases – very versatile substrates for further chemical transformations.
The selective nitration of meso-tetraphenylporphyrin complexes is described. The reaction of the above porphyrinates with 25% HNO 3 or 5% HNO 3 at room temperature or 0-5 °C, respectively, results in the formation of the corresponding mono b-nitroporphyrins (56-81%), accompanied by small amounts of a mixture of b,b-dinitro by-products. The results described above are the first known examples of b-mononitration of meso-tetraarylporphyrin complexes under electrophilic conditions. Reactions with nickel(II), copper(II), and cobalt(II) porphyrinates are discussed.The selective derivatization of easily available meso-tetraarylporphyrins is of significant importance due to their potential use as photosensitizers in Photodynamic Therapy (PDT 1 ), molecular-based multi-bit memory storage, 2 electron-donor parts in various artificial photosynthetic models, 3 etc.Previous studies 4 in metalloporphyrins have shown that the position of substitution, and especially the yield, can be controlled by varying the co-ordinated metal in the porphyrin core ring when nitrating (under radical conditions) with nitrogen dioxide. When metals with a higher electronegativity were used, a corresponding increase in the amount of b-nitrated products was observed. b-Nitration was thus main route for Co II , Cu II , Ni II , and Pd II complexes. In each of these reactions, small amounts (less then 5%) of dinitrated compounds were also obtained. 4a However, in small scale, from the preparative point of view, a serious inconvenience of this reaction is providing NO 2 ; it is rather difficult to assure the proper amount of gaseous nitrogen dioxide, or to prepare the desired solution of NO 2 (for example in hexane) for the reaction -hence, instead of mononitration, the formation of a complicated mixture of mononitro-, various isomers of dinitro-, and even trinitro-products was observed. In some cases, as a side-process, the core ring-opening, yielding the bilinone, was also mentioned. 4a The latter process resulted from an initial attack at a meso-position. Due to these reasons, other methods were sought, which avoided operations with inconvenient and relatively expensive 5 nitrogen dioxide.In 1997, an example of b-mononitration with the use of Cu(NO 3 ) 2 was reported, 6a but no experimental details were provided. An earlier paper 6b described this type of puzzling nitration for zinc(II) meso-tetraphenylporphyrin under similar conditions [with tallium(III) nitrate or with cerium(IV) ammonium nitrate] leading directly to the free bases; however, with moderate or low yield.It is well known that meso-tetraphenylporphyrin (TPP) and its derivatives (as free bases) can be efficiently nitrated with the use of yellow or red nitric acid to give substitution products in meso-aryl rings. 7 A more recent example of this process, involving the NaNO 2 /TFA system, gave similar results. 8 One can suppose that the reactivity and the reaction course could be changed herein, when the same electrophilic conditions will be applied for the metalloporphyrin moieties ( Fig...
The synthesis, chromatographic isolation, and structure elucidation of β,β-substituted isomers of dinitro-5,10,15,20-tetraphenylporphyrin complexes are described. meso-Tetraphenyl-porphyrin chelates (CuII, NiII, CoII) upon reaction wit e.g., nitric acid (yellow HNO3, d = 1.52, diluted to 25–50%) in CHCl3 formed a mixture of nitro-derivatives with combined yields of ca 80%. This nitration (under optimized conditions: 25–30% HNO3, 30–40 min, r.t.) can be carried out selectively to give mainly β,β-dinitro-compounds in yields of up to 73%. From the above mixtures of five possible regioisomers that can be formed, usually two or three of them were isolated, for which the structures were assigned on the basis of 1H NMR spectra including COSY and NOESY measure-ments. These types of products are attractive starting materials for synthesis of potential anticancer PDT agents with unique structures, being practically unavailable by any other alternative method.
An efficient synthesis of functionalized fused pyrimidine derivatives from the respective ortho-(isocyanomethyl)nitroarenes is described: hydrolysis of the isocyano group in the title isocyanides followed by catalytic reduction of the nitro group and subsequent cyclocondensation of the diamine formed with orthoesters leads to the final products.
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