Pyridine-2-carboxy late

All four isomeric selenolopyridines which can be derived from benzoselenophene (423— 426 Scheme 123) have been described. Ethyl 3-hydroxyselenolo[2,3-fe]pyridine-2-carboxy-late (429) has been prepared as shown in Scheme 124 (73BSF704). Treatment of ethyl 2-chloropyridine-3-carboxylate with methaneselenol yields (427). Nucleophilic displacement of bromine in bromoacetic acid with subsequent loss of methyl bromide yields (428), which after esterification is cyclized under Dieckmann conditions to give (429). The parent compound (423 colorless oil with b.p. 92 °C/1 mmHg) is prepared either by cyclization of compound (430) and subsequent decarboxylation of the intermediate acid (equation 57) or by reduction of 2-nitroselenophene and subsequent condensation of the amino compound with malonaldehyde bis(diethyl acetal) in the presence of zinc chloride (equation 58) (76BSF883). Selenolo[3,2-6]pyridine (426 b.p. 127-129°C/10 mmHg m.p. 35.5-37.0°C) has been obtained in an analogous manner. 

The 977-pyrido[3,4- ]pyrrolizin-9-one 145 has been prepared for its photochemical properties. The preparation involves an intramolecular Friedel-Crafts acylation of the acid chloride formed from 3-(l-pyrrolyl)pyridine-4-carboxy-late (Scheme 40). The product is a photosensitizer, which absorbs visible light its absorption spectra are pH, solvent, and concentration dependent <1994SAA57>. 

Cycloadditions are in general an effective way of constructing cyclobutane rings. A wide variety of heterocyclic systems dimerize in this way. 1,3-Diacetylindole, for example, affords the head-to-tail dimer 242 on irradiation in ethanol.185 Ethyl 2-ethoxy-l,2-dihydroquinoline-l-carboxy-late is similarly converted in diethyl ether into the trans head-to-head dimer.186 Notable among many analogous photodimerizations are those reported in 1,4-dihydropyridines,187 in furo[3,2-b]pyridin-2(4//)-ones,188 in 8-methyl-s-triazolo[4,3-a]pyridine,189 and in 2H-2-benzazepine-1,3-diones.190 The [ 2 + 2] dimerization of amidopyrine is the first reported example of a photocycloaddition in a 4-pyrazolin-3-one.191... 

This procedure is also efficient for the synthesis of other fused tetrazoles, such as ethyl l,5-dihydro-5-oxo-7-phcnyl-8-(phenylsulfonyl)tetrazolo[ 1,5- pyridine-6-carboxy late <2000J(P1)3686>. At the same time, the unexpected azido-tetrazolo tautomerization and reversible tetrazolo transformation of 3,6-diazido-l,2,4,5-tetrazine are remarkable compared to all other polyazido heteroaromatic high-nitrogen C-N compounds <2005JA12537>. 

The inert hydroxo-bridged species were also a product of (very fast) hydrolysis of p-cymene osmium complexes with glycinate, L-alaninate, a-aminobutyrate and p-alaninate. However, complexes with picolinate as the chelating ligand, [Os(r 6-/> cym)Cl(pic)] 8 and [Os(r 6-biph)Cl(pic)] 9, with pyridine as /V-donor and carboxy-late as O-donor, hydrolyzed with half-lives of 0.20 and 0.52 h (298 K), and aqua adduct pKa values (pk L value for solutions in D20) of 6.67 and 6.33, respectively. Complexes 8 and 9 were cytotoxic towards A2780 human ovarian cancer cells, with IC50 values of 8 and 4.2 pM, respectively [64],... 

Coprecipitation of yttrium, copper and barium is most often done with carboxy-lates (citrates, oxalates, acetates) from solutions of nitrates. Control of the pH, temperature and concentration make the precipitation as quantitative as possible in order to preserve the stoichiometry of the mixture [126-129]. Long-chain carboxy-lates (2-ethylhexanoate, neodecanoate) ensure the solubility of metals in volatile solvents such as xylene or xylene-pyridine mixtures, in order to make drying at... 

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