3243-01-4Relevant articles and documents
Lariat-type B12 model complexes. 1. New pendant methylpyridyl costa-type organocobalt complexes provide insight into the role of the axial ligand in butterfly bending and redox properties
Gerli, Alessandra,Sabat, Michal,Marzilli, Luigi G.
, p. 6711 - 6718 (1992)
A new B12 (cobalamin, Cbl) model system with the potentially quinquedentate ligand, 2,3,9,10-tetramethyl-6,2-pyridylmethyl-1,4,8,11-tetraazaundeca-1,3,8,10-tetraen- 1,11-diolo (C1py), has unique properties attributable to the coordinated pendant pyridine, which is attached covalently at the 2-position by a one-methylene link to the central C of the propylene chain of (DO)(DOH)pn (N2N2′-propanediylbis(2,3-butanedione 2-imine 3-oxime)). Treatment of C1py, constructed from the new diamine, 2-(2-pyridylmethyl)-1,3-propanediamine, with hydrated CoBr2 afforded [BrCo(C1py)]ClO4 (5). From 5, salts of [XCo(C1py)]+ (X = CN, N3, Cl) and of [RCo(C1py)]+ (R= CH3, i-C3H7, neo-C5H11 CH2CF3) were synthesized by substitution and by oxidative addition of RX to in situ generated Co-(C1py), respectively. In contrast to previous model systems, the C1py model behaves more like Cbls; for example, no dicyano complex was obtained. Coordination of the pyridyl moiety in the C1py derivatives is confirmed by X-ray structural analysis of [ClCo(C1py)]PF6 (7) and [CH3Co(C1py)](ClO4/BF4) (9a). The pendant arm forces the pyridine to adopt an orientation 90° different from that in the [pyCo((DO)(DOH)pn)Cl(or R)]PF6 derivatives. This new orientation greatly decreases butterfly bending, a structural feature relevant to triggering of Co-C bond homolysis by B12 enzymes. This result is strong evidence that a planar N-donor ligand can induce butterfly bending. In 7 the axial Co-N distance is 1.959 (4) A?, shorter than this distance (2.06 (1) and 2.07 (1) A?, for two independent molecules) in 9a and similar to that in [pyCo((DO)(DOH)pn)Cl]PF6. Although electrochemical reduction of the latter was not reversible, the reversible formation of Co(II) and Co(I) species from 7 (and 5) can be attributed to the pendant nature of the axial pyridine. The Co(III)/Co(II) redox couple was more cathodic for 7, consistent with better electron donation by the pendant pyridine. The Co(II)/Co(I) redox potential (-1.0 V vs 0.01 M Ag+/Ag) of 7 and 5 was similar to that for nonalkyl (DO)(DOH)pn derivatives, which lack a pendant base; this suggests that Co(II)/Co(I) reduction in nonalkyl C1py derivatives proceeds through a base-off form in which the Co-pyridine interaction is weak, at best. Such a mechanism was proposed previously for Cbls. For both [CNCo(C1py)]ClO4 and cyanoCbl (vitamin B12), a single two-electron wave was observed upon reduction. For alkylC1py derivatives, only one cathodic wave was observed upon reduction. Just one prominent cathodic peak has been reported for alkylCbls. For [CH2Co(C1py)]ClO4 (9), reduction formed a dealkylated Co(I) species, which was oxidized to Co(II) on the reverse anodic scan. Similarly, dealkylated Co(I) species formed after one-electron reduction of alkylCbls, including methylCbl, are oxidized to Cbl(II) in the return anodic scan. The Co(III)/Co(II) reduction potentials of C1py and Cbl derivatives were influenced nearly identically by changes in the axial ligand; for R(or X) = solvent, Cl, CN, neo-C5H11, CH3, an excellent correlation with a slope of unity was obtained. The simpler chemistry of the C1py derivatives, as illustrated here by electrochemical studies, makes them excellent models to study fundamental chemistry relevant to Cbls.
A synthesis of N-bridged 5,6-bicylic pyridines via A mild cyclodehydration using the Burgess reagent and discovery of A novel carbamylsulfonylation reaction
Li, Jie Jack,Li, James J.,Li, Jun,Trehan, Ashok K.,Wong, Henry S.,Krishnananthan, Subramanian,Kennedy, Lawrence J.,Gao, Qi,Ng, Alicia,Robl, Jeffrey A.,Balasubramanian, Balu,Chen, Bang-Chi
supporting information; experimental part, p. 2897 - 2900 (2009/05/30)
(Chemical Equation Presented) Cyclodehydration using the Burgess reagent provided a novel approach toward the synthesis of N-bridged 5,6-bicylic pyridines including pyrolo-, imidazo-, and triazolopyridines under mild and neutral conditions. The methodology tolerates acid-sensitive functional groups. A novel addition product was observed between the resulting pyrrolo- or imidazopyridine and an additional equivalent of the Burgess reagent, producing the corresponding sulfonylcarbamate adduct.
Tartronic acids, their acetalic ethers and O-esters
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, (2008/06/13)
Tartronic acid acetalic ethers and esters of the general formula: STR1 are provided and are useful in treatment of bone dysmetabolism. As examples, Ra and Rb may be hydrogen, B is a C2 -C12 acyl group, R is phenyl and n is 0-12.
Oxidation of Diethyl (Pyridylmethyl)malonates with Mn(III) Acetate, Ce(IV) Ammonium Nitrate, and Iron(III) Perchlorate in the Presence of Alkenes and Alkynes
Citterio, Attilio,Sebastiano, Roberto,Carvayal, Magaly Caceres
, p. 5335 - 5341 (2007/10/02)
The oxidation of substituted diethyl 2-,3-, or 4-picolylmalonates (1a-g) by Mn(III) acetate in acetic acid, Ce(IV) ammonium nitrate in methanol, and Fe(III) perchlorate in acetonitrile in the presence of substituted alkenes (2) and alkynes (3) affords substituted tetra- or dihydroquinolines and/or isoquinolines (4-9) in good to excellent yield.The influence of reaction medium on yield and isomer distribution has been investigated.A mechanism involving oxidative deprotonation of malonic esters by high-valent metal salts to malonyl radicals, their addition to olefins, and intramolecular homolytic substitution to protonated or metal-complexed heteroaromatic bases by the resulting substituted carbon radicals is suggested.
