Joseph M. Tanski

Aza-crown macrocycles as chiral solvating agents for mandelic acid derivatives.

A series of new chiral macrocycles containing the trans-1,2-diaminocyclohexane (DACH) subunit and arene- and oligoethylene glycol-derived spacers has been prepared in enantiomerically pure form. Four of the macrocycles have been characterized by X-ray crystallography, which reveals a consistent mode of intramolecular N-H···N hydrogen bonding and conformational variations about the N-benzylic bonds. Most of the macrocycles were found to differentiate the enantiomers of mandelic acid (MA) by (1)H NMR spectroscopy in CDCl(3); within the series of macrocycles tested, enantiodiscrimination was promoted by (i) a meta-linkage geometry about the arene spacer, (ii) the presence of naphthalene- rather than phenylene-derived arene spacers, and (iii) increasing length of the oligoethylene glycol bridge. (1)H NMR titrations were performed with optically pure MA samples, and the data were fitted to a simultaneous 1:1 and 2:1 binding model, yielding estimates of 2:1 binding constants between some of the macrocycles and MA enantiomers. In several cases, NOESY spectra of the MA:macrocycle complexes show differential intramolecular correlations between protons adjacent to the amine and carboxylic acid groups of the macrocycles and MA enantiomers, respectively, thus demonstrating geometric differences between the diastereomeric intermolecular complexes. The three most effective macrocycles were employed as chiral solvating agents (CSAs) to determine the enantiomeric excess (ee) of 18 MA samples over a wide ee range and with very high accuracy (1% absolute error).

Remarkable stereoselectivity in the alkylation of a hydroazulenone: progress towards the total synthesis of guanacastepene

Abstract exo-Methylene ketone 6 serves as a vehicle for elaboration of the C8 quaternary center en route to guanacastepene via a conjugate addition–alkylation sequence. Methylation of the cycloheptadienolate derived from 7 is highly selective for the desired relative stereochemistry, as determined by NMR and crystallographic analysis.

Tin(IV) and organotin(IV) derivatives of novel β-diketones I. Dialkyltin(IV) complexes of 1-phenyl-3-methyl-4-R′(CO)-pyrazol-5-one (R′ = CCl3, OCH3, OC2H5, OiC3H7, OC7H7). Crystal and molecular structure of trans-dimethylbis]1-phenyl-3-methyl- 4-i-propoxycarbonyl-pyrazolon-5-ato]tin(IV)

Abstract Stable six-coordinate tin(IV) and organotin(IV) derivatives R2SnQ∗*2 (R = Me, Et, Bun, Bu1) ( HQ ∗* = 1- phenly -3- methyl -4- trichloracetyl-pyrazol -5- one ) have been synthesized in basic (triethylamine0 solution of chloroform. These complexes have been characterized by elemental analysis and spectroscopic (IR and far-IR, 1H, 13C and 119Sn NMR) data. In basic (KOH) alcoholic R′OH solutions (R′ = Me, Et, Pri, benzyl), the tin acceptor induces cleavage of the CCCl3 bond in the donor (Q∗*)− and the new derivatives bis(1-phenyl-3-methyl-4-alkoxycarbonyl-pyrazolon-5-ato)R2Sn(IV) (R = Me, Et, Bu1 or Bua) and (1-phenyl-3-methyl-4-ethoxycarbonyl-pyrazolon-5-ato)-Me2Sn(IV)Cl have been obtained. Structural information has been derived from 119Sn NMR parameters such as 1 J( 119 Sn  13 C ), 2 J( 119 Sn  1 H ) and δ(119Sn). The diffraction study of the complex [Me2Sn(1-phenyl-3-methyl-4(COOPr1)-pyrazolon-5-ato)2] shows the metal to be six-coordinate in a skewed trapezoidal bipyramidal (STB) geometry; SnO distances are 2.10(1) and 2.39(1) A in one ligand, and 2.09(1) and 2.39(1) A in the other ligand, and the MeSnMe bond angle is 157.0(8)°. The title compound crystals are monoclinic, space group P21/c, cell parameters: a = 11.489(4), b = 14. 558(7), c = 18.973(8) A , β = 77.14(3)° .

Hetero-multinuclear Ruthenium(III)/Platinum(II) Complexes That Potentially Exhibit Both Antimetastatic and Antineoplastic Properties

Hetero-multinuclear, platinum/ruthenium species were synthesized and tested for their effect on the motility of A549 (nonsmall cell lung) and MDA-MB-231 (breast) cancer cells and for their ability to inhibit DNA mobility using gel electrophoresis. It was found that the Ru(2)Pt trinuclear species [Na(2)]{[Ru(III)Cl(4)(DMSO-S)(-μ-pyz)](2)Pt(II)Cl(2)}, AH197, was much more efficient at inhibiting cell motility than [C(3)N(2)H(5)][Ru(III)Cl(4)(DMSO-S)(C(3)N(2)H(4))], NAMI-A, while the dinuclear RuPt species [K][Ru(III)Cl(4)(DMSO-S)(-μ-pyz)Pt(II)(DMSO-S)Cl(2)], IT127, was slightly better than NAMI-A. However, the dinuclear species retarded the electrophoretic mobility of DNA greater than both the trinuclear complex and cisplatin. The metal complexes and their respective BSA protein/metal adducts were studied by X-ray absorption spectroscopy. The spectra led to the conclusion that BSA donor atoms have substituted for the chloride ligands and perhaps the DMSO ligands.

Designing ionic liquids with boron cluster anions: alkylpyridinium and imidazolium [nido-C2B9H11] and [closo-CB11H12] carborane salts

A range of new alkylpyridinium and imidazolium carborane salts with [nido-C(2)B(9)H(12)](-), [closo-CB(11)H(12)](-), and [RC(2)B(11)H(11)](-) (R = methyl or butyl) anions have been prepared and characterized by physical and thermal methods, including the solid state structures of five of the salts determined by single crystal X-ray diffraction. The tendency of the salts to form low-melting ionic liquids has been assessed; all the salts studied with [nido-C(2)B(9)H(12)](-) anions melted below 100 degrees C and, significantly, have melting points that are 25-85 degrees C lower than those of the corresponding [closo-CB(11)H(12)](-) analogs, demonstrating that a wider range of boron-rich ionic liquid materials can be readily accessed.

Cobalt tris(mercaptoimidazolyl)borate complexes: synthetic studies and the structure of the first cobaltaboratrane

The paramagnetic complexes (TmtBu)CoX (X = Cl, Br, I) have been readily prepared and structurally characterized and provide a convenient entry into cobalt(II) tris(mercaptoimidazolyl)borate chemistry. A number of derivatives, including mononuclear triphenylphosphine adducts [(TmtBu)Co(PPh3)]X and dinuclear compounds [Co2(TmtBu)2X]Y, have been prepared in order to ascertain whether cobalt is a reliable surrogate for zinc in biological systems, particularly in sulfur-rich coordination environments. The structure of the first cobaltaboratrane is also reported.

Synthesis and structural characterization of 2-mercapto-1-tert-butylimidazole and its Group 12 metal derivatives (HmimtBu)2MBr2 (M = Zn, Cd, Hg)

Abstract2-Mercapto-1-tert-butylimidazole (HmimtBu) and its Group 12 metal complexes (HmimtBu)2 MBr2 (M = Zn, Cd, Hg) have been readily prepared and structurally characterized. Whereas the former displays a dimeric structure in the solid state with two S ⋅ ⋅ ⋅ H–N interactions linking each pair of molecules, the four-coordinate complexes exhibit distorted tetrahedral geometries with the S–M–S angles in the range 103.2–135.2○. The average M–Br bond lengths are 2.401, 2.567, and 2.688 Å for M = Zn, Cd, and Hg, respectively, and the corresponding average M–S bond distances are 2.350, 2.540, and 2.467 Å. The average C–S bond length for all the complexes (1.72 Å) is only ca. 0.02 Å longer than the corresponding value in the free ligand. HmimtBu is orthorhombic, space group Pbca, a = 10.1571(5) Å, b = 9.7906(5) Å, c = 17.6616(9) Å, V = 1756.34(15) Å3, Z = 8; (HmimtBu)2ZnBr2 is monoclinic, space group C2/c, a = 17.187(3) Å, b = 8.9908(17) Å, c = 15.560(3) Å, β = 117.206(3)○, V = 2138.3(7) Å3, Z = 4; (HmimtBu)2CdBr2 is triclinic, space group P

Development of a 2-Aza-Cope-[3+2] Dipolar Cycloaddition Strategy for the Synthesis of Quaternary Proline Scaffolds

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