Towards a novel switchablearomatic hemiporphyrazineChemistry Department, Gustavus Adolphus College, Saint Peter, MN
Our research group has an interest inphthalocyanine molecules with lowsymmetry (e.g., two-fold) Linear conductive polymers Functional supramolecularstructures Solar energy Photodynamic cancer therapyNNNNNNNN M
Hemiporphyrazines have two-fold symmetry However, they are 36 π e–, and not aromaticNNH2 NH2CNCN+NN NNHNNHNNNHNHNHor
Oxidation of a dicarbahemiporphyrazine from 36π e– to 34 π e–, creating an aromatic ringN NNHNNHNOH OHOH OHUchiyama, M., et al. J. Am. Chem. Soc. 2012, 134, 190-193; Ziegler, C. J., et al. New J.Chem. 2011, 35, 794-799, Eur.J. Inorg. Chem. 2010, 775-780.N NNHNNHNOH OOH O
Synthesize a hemiporphyrazine ring withhydroxyl groups that can be oxidizedNNH2 NH2OH OHCNCN+NN NNHNNHNNOH OHOH OHNHNHNHorNN NNHNNHNNO OHO OHDDQ
Synthesis of 2,6-diamino-3,5-dihydroxypyridineNNH2 NH2 NNH2 NH2I INNH2 NH2OH OH10% HCl3 h reflux94%I2/KI(aq)20 h72%Bojarska-Dahlig, H. Rocz. Chem. 1957, 31, 1041-1045.
Our attempt at reproducing the method:~ 1:1Applying a 2:1 I2/KI : pyridine ratio in the synthesis,instead of the prescribed 1:1 ratio gave the desiredproduct directly in 97% yield.NNH2 NH2 NNH2 NH2I II2/KIH2O20 h+NNH2 NH2I
Our attempts at hydrolysis of 2,6-diamino-3,5-diiodopyridine:NNH2 NH2I INNH2 NH2I OH10% HCl3 h refluxNNH2 NH2I OHNNH2 NH2OH OH10% HCl3 days reflux25 % yield
NNH2 NHHBHCHAHA1NNH2 NIHBHCHAHA2NNH2 NIHBIHAHA3NNH2 NIHBOHAHAHC4NNH2 NOHBOHAHAHCH51-C 1&2-A1-B2-B 2-C3-A3-BProduct from originaliodination procedureProduct from revisediodination procedureProduct from originalhydrolysis procedureProduct from revisedhydrolysis procedure3-A3-B4-B4-C 4-A/5-C5-A5-B5-C5-A5-B
Other approaches to the synthesis of 2,6-diamino-3,5-dihydroxypyridine have been explored, including thefollowing reactions: Reaction of 2,6-diamino-3,5-diiodopyridine with 30% H2O2 inboth neutral and 3 M HCl solution; Reaction of 2,6-diamino-3,5-diiodopyridine with KOH or CsOHin the presence of CuI with and without a cation exchange resin; Reaction of 2,5-diaminopyridine with conc. HNO3 and H2SO4acids and KBr; Reaction of 2,5-diaminopyridine with potassiumperoxydisulfate (K2S2O8) and KOH (Boyland-Sims reaction).However, none of these reaction schemes have to dateproduced significant results.
We are also exploring the sulfur analogue ofthese compounds:NNH2 NH2Br2MeOH+ NH4SCNNNH2 NH2NCS SCNNNH2 NH2SH SH1) Na2S (aq)2) HOAcReed, R.W., et al. J. Am. Chem. Soc. 2002, 124, 9498-9509.
The approach to the synthesis oftetrahydroxyhemiporphyrazines revealedunexpected complications in the reportedsynthesis of the key precursor, 2,6-diamino-3,5-dihydroxypyridine. We have modifiedthese procedures to give the desiredcompound. Investigation into the formation of thehemiporphyrazine ring is being undertaken.