Kay D. Onan

Intramolecular Diels-Alder reactions with furan: the gem-dialkyl effect revisited

Abstract Remote substituents that influence ground state state rotamer populations were found to be important controlling factors in the intramolecular Diels-Alder reaction with furan.

Transmetallation reactions of tetranuclear copper(II) complexes. I. Crystal and molecular structures of an intermediate and a final product of reaction of di-μ-oxo-tetra[chloro(DENC)copper(II)],(DENC = N,N-diethylnicotinamide) with [Zn(N2S2], (N2S2 = diacetyl-bis-hydrazonato-S-methyl-carboditithioate) in aprotic solvents

Abstract Di-μ-oxo-tetra[chloro(DENC)copper(II)],[(DENC)CuCl]4O2, (DENC) = N,N-diethylnicotinamide) reacts with two moles of dimeric [Zn(N2S2]2), (N2S2 = diacethyl-bis-hydrazonato-S-methyl-carbodithioate) to give 2 moles of [Cu(N2S2]2 and a variety of zinc containing products, including zinc(II) oxide. The crystal and molecular structures of the intermediate five-coordinate complex Zn(N2S2)(DENC), A, and a final product, di-μ-(N,N-diethylnicotinamide-O,N)-tetrachlorodizinc(II), B, from this interesting metal exchange reaction are reported. Although the ultimate products are the same, no intermediate analog of A is detected with monomeric tetrahedral Zn(NS)2 reactants. Complex A crystallizes in the triclinic space group P 1 with Z = 2 in a cell of dimensions a = 10.258(1), b = 10.708(1), c = 12.548(1) A, α = 107.69(1), β = 99.70(1), γ = 106.49(1)°. Complex B also crystallizes in space group P1 with Z = 2 but in a cell of dimensions a = 9.427(4), b = 14.106(6), c = 8.589(3) A, α = 120.87(3), β = 116.17(3), γ = 106.76(3)°.

SYNTHESIS, STRUCTURE AND PROPERTIES OF THE ISOMERIC DINUCLEAR COMPLEXES ((DENC)2CUX2)2 (DENC = N,N-DIETHYLNICOTINAMIDE; X = CL OR BR) AND THE KINETICS OF THEIR REACTIONS WITH DENC IN METHYLENE CHLORIDE

Abstract Tetrahalo - tetrakis - (N,N-diethylnicotinamide)dicopper(II) species [(DENC) 2 CuX 2 ] 2 (X = Cl or Br) differ in that while the chloro complex is bridged by two DENC molecules in the solid but two chloro groups in solution, the bromo complex is always bromo-bridged. These conclusions result from an X-ray structural determination of (DENC)Cl 2 Cu(DENC,DENC)CuCl 2 (DENC) and from spectroscopic comparisons. The kinetics of conversion of the respective dimers to monomeric (DENC) 3 CuX 2 species have been measured in methylene chloride solution.

Crystal and molecular structures of three M(NS)2 transmetalating agents (NS is a monoanionic S-methyl hydrazinecarbodithioate Schiff base; M = Co, Zn)

Abstract The crystal and molecular structures of the M(NS) 2 transmetalating agents bis-(S-methyl-isopropylidenehydrazinecarbodithioato) cobalt(II), its zinc analog and of bis-(S-methyl-benzylidenehydrazinecarbodithioato) zinc(II) are reported. Structural differences which may give rise to different mechanisms of transmetalation are noted.

The crystal and molecular structure of trimeric [L2CuCl2]3, L=N,N-diethylnicotinamide

Abstract The complex prepared with a 2:1 molar ration of L = N,N-diethylnicotinamide to anhydrous copper(II) chloride has been crystallized from ethanol as the trimeric unit [L2CuCl2]3. The crystals are monoclinic, space group P21/c with a = 16.618(1), b = 8.253(2), c = 28.194(1) A, β = 117.3(4)°. The trimeric unit utilizes a crystallographic center of symmetry. Least squares refinement of the structure using 3692 independent intensities has yielded an R factor of 0.059. Each molecule consists of two five-coordinate and one six-coordinate copper center. The μ,μ-dichloro bridging system is asymmetric with a Cu⋯Cu separation of 3.686 A. The CuN distances range from 2.004(4) to 2.027(4) A and the CuCl distances from 2.264(2) to 2.982(-) A. The copper coordination spheres are compared to that in (py2CuCl2).

Stoichiometry and products of transmetalation of dimeric copper(I) complexes L2Cu2X2 (L is an N,N,N′,N′-tetraalkylethylenediamine; X = Cl or Br) by M(NS)2 reagents in aprotic solvents

Abstract Dimeric copper(I) complexes L 2 Cu 2 X 2 react with 1 and 2 mol of M(NS) 2 reagents in aprotic solvents to give quantitative yields of products LMX 2 and (NS)M(X,X)M(NS), respectively. Here, L = N,N,N′N′ -tetraethylethylenediamine, X = Cl or Br, M = Co, Ni, Cu and Ns = S -methylisopropylidenehydrazinecarbodithioate. Dimers (NS)Cu(X,X)Cu(NS) are oxidatively unstable. LCoCl 2 crystallizes in the monoclinic space group P 2 1 / c (C 2h 5 ): a = 7.345(1), b = 11.801(1), c = 17.478(2) A, β = 104.98(1)°, Z = 4. The electronic spectra of LMX 2 and (NS)M(X,X)M(NS) complexes are discussed.

Crystal and molecular structure of racemic fac-tris-(S-methylisopropylidene-hydrazinecarbodithioato)cobalt(III), Co(NS)3, and the kinetics of its isomerization in aprotic solvents

Abstract The crystal and molecular structure of fac-tris- (S-methylisopropylidenehydrazinecarbodithioato)cobalt (III) is reported. The dark olive-green Co(NS)3 crystallizes in the monoclinic space group P21/c with Z = 4 in a cell of dimensions a = 17.876(2), b = 9.792(2), c = 14.816(2) A and β = 108.63(1)°. The coordination sphere is relatively undistorted but the cobalt atom does not lie in the center of this sphere. Kinetic studies have shown the fac to mer isomerization to have a very large (⩾100) equilibrium constant and to proceed by a trigonal twist mechanism.

Regioselective hydrocarboxylations of olefinic amines: characterization of a key intermediate

Abstract Homoallylic and bishomoallylic amine bidentate rhodium (I) complexes undergo regioselective hydrocarboxylations and give rise to amino esters or lactams.

Novel synthesis of 2-fluoroestradiol from 19-Cortestosterone: Biomimetic oxidative defluorination to 2-hydroxyestradiol

A new, short synthetic route to 2-fluoroestradiol from 19-nortestosterone is described which gives the target compound in an approximately 25% overall yield. Oxidative defluorination of 2-fluoroestradiol to 2-hydroxyestradiol via treatment with Frémys salt/iodide ion is reported. This process is regarded as biomimetic with respect to cytochrome P-450-dependent oxidative defluorination.

Effect of conformation and stereochemistry in substitution reactions of fused chlorocyclobutanones: oxyallyl cation intermediates

Abstract Fused α-acyloxycyclobutanones, whose conformation and stereochemistry have been unambiguously established by X-ray analysis, undergo an unusual displacement with methoxide as nucleophile to produce α-methoxycyclobutanones. The success of this reaction, which suggests the intermediacy of an oxyallyl cation, is highly dependent on conformational and steric factors.