Embedded units in conjugated polymers

The problem of embedding of several monomeric units (benzene, thiophene, isothianaphthene) into linear oligoenes or into a polymer built up by the same units is discussed. Using a simple model Hamiltonian, we evaluate the geometry (bond lengths) and electronic structure (energy gaps) of conjugated oligomers containing up to 200 atoms. Special attention is paid to end effects. The quinoid-aromatic transition and the conjugation interruption due to embedded defects is studied in some detail.     

Synthesis and characterization of Cu,Ni and Zn binding capability of some amino- and imidazole hydroxamic acids: Effects of substitution of side chain amino-N for imidazole-N or hydroxamic-N-H for -N-CH3 on metal complexation

Solution equilibrium studies on Cu(II)-, Ni(II)- and Zn(II)-N-Me-β-Alaninehydroxamic acid (N-Me-β-Alaha), -N-Me-α-alaninehydroxamic acid (N-Me-α-Alaha), -Imidazole-4-carbohydroxamic acid (Im-4-Cha), -N-Me-imidazole-4-carbohydroxamic acid (N-Me-Im-4-Cha) and -Imidazole-4-acetohydroxamic acid (Im-4-Aha) systems have been performed by pH-potentiometry, UV–Vis spectrophotometry, EPR, CD, ESI-MS and ¹H NMR methods. According to the results: (i) the amino-N atoms are more basic in N-Me-α-Alaha and N-Me-β-Alaha than the hydroxamate function, but the trend is just the opposite between the imidazole-N(3) and hydroxamate. (ii) The metal ion anchor is always the hydroxamate part in the amino acid derivatives, while it is always the imidazole-N(3) in the studied imidazolehydroxamic acids. (iii) The three studied N-Me derivatives do not form metallacrowns. Only hydroxamate type chelate is formed with N-Me-β-Alaha, but with N-Me-α-Alaha a new type of coordination mode (via amino-N and hydroxamate-O) also exists. N-Me-Im-4-Cha also forms a dinuclear complex, [M₂L₃], with Cu(II) and Ni(II) (but not with Zn(II)). In this complex, one of the three ligands might bridge the two metal ions (five-membered hydroxamate-(O,O) plus five-membered (N_im, O_carb) bridging bis-chelating mode), while each of the additional two ligands binds to one metal. (iv) The two studied N–H derivatives, having dissociable proton on the hydroxamic-N, are able to form metallacrown species. A pentanuclear complex, [M₅L₄H₋₄], is exclusively formed above pH 4 between Cu(II) and Im-4-Aha. Interestingly, this 12-metallacrown-4 type complex, although together with various mononuclear binding isomers, appears also with Ni(II) and Zn(II). Unfortunately, the complexes of Im-4-Cha are not soluble in water at physiological pH at all.     

A Stereoselective Synthesis of (±)-cis-γ-Irone

(±)-cis-γ-Irone( 1 ), a main constitutent of natural iris oil, has been stereoselectively synthesized from methyl (2E)-3 -[(2,2,4-trimethyl-3-cyclohexen-1-yl)methoxy]-2-propenoate (3) (6 steps, overall yield 14%). The cis-configuration as the exocyclic position of the double bond of 1 were secured by the thermal ene reaction of the β-(alkenyloxy)acrylate 3 yielding the 3-oxabicyclo [3,3,1] nonane derivative 5 .     

Synthese yon 2,6-Diencarbonsäuren Vorläufige Mitteilung

Through sequential Claisen- and Cope rearrangements the chainlengthening of allylic alcohols by one isoprene unit was achieved. Treatment of (E)-1a first with lithium N-cyclohexyl-N-isopropylamide at ?70°, followed by trimethylsilylchloride and warming up to room temperature yielded after work-up 3a (R = H), which rearranged at 156° in high yield to (E/Z)-4a. An analogous reaction sequence transformed 6 to 8. Choosing lithium N-methylanilide as a base (E/Z)-9 was selectively rearranged to 12, which was converted to the Cecropia juvenile hormone precursor (E/Z)-4b.     

An efficient ab initio gradient program

An ab initio Hartree-Fock gradient program is described. It is characterized by (1) efficiency of the gradient evaluation, and (2) capability of handling higher angular momentum (d andf) basis functions. The latter are constructed from shifted Cartesian Gaussian p-type primitives. A satisfactory solution is presented for the problems connected with the neglect of small integrals in a gradient program. Methods for increasing the efficiency of the SCF procedure are discussed.     

The stereoselective α-alkylation of chiral β-hydroxy esters and some applications thereof

The stereoselectivity of the α-alkylation of chiral β-hydroxy ester is discussed. The configuration of the alkylated product was proved chemically (Scheme 2). A one pot aldol-alkylation reaction was developed leading stereoselectively to racemic (s*,s*)-α-alkyl-β-hydroxy ester (Scheme 3,4). Baker's yeast reduction of 2-alkyl-3-keto ester led to valuable chiral (2RS,3S)-intermediates, which were converted via the corresponding dianion to compounds with a chiral quaternary C atom (Scheme 6). Synthetic applications of the above findings are shown in the synthesis of various chiral compounds (Scheme 8 and 9).     

Thermisches Verhalten von Cyclopropa[c]chromenen

The Cyclopropa[c]chromenes 14 , trans-and cis- 15 , trans-and cis- 16 and 17 rearrange on heating > 200° in N, N-diethylaniline to give 2-alkyl-2H-chromenes 7, 8, 21, 22. The rate determining step of this rearrangement is the ‘homoelectrocyclic’ ring opening of the cyclopro-pa[c]chromenes to give ω-allyl-quinomethanes of type 4. These intermediates show fast [1,5s] and [1,7a] H-shifts, followed by electrocyclic ring closure. Deuterium labelling experiments are in agreement with this mechanism. The remarkable dependence of the rates of rearrangement with respect to the stereochemistry of the cyclopropa[c]chromenes (cf. table 2) suggests that in the first step only one of the two possible disrotatory modes of ring opening is involved.     

On triazoles. VII Synthesis of novel tri- and tetracyclic ring systems

The ring-closure of the 5-amino-1-(2-aminophenyl)-3-methylthio-1H-1,2,4-triazole derivatives 3 and 4 with different simple and cyclic C₁ components lead to the formation of 1,2,4-triazolo[1,5-α]-1,3,5-benzotriazepines 5–6 , their 4,5-dihydro- 7 , different 5-spiro-homocyclic- 8–13 , and 5-spiro-heterocyclic- 14-15 analogues. The structure of the compounds obtained was proved with the use of their ir, uv, ¹H-nmr and ¹³C-nmr spectra.     

Nitrogen bridgehead compounds part 14. Acylation of ethyl 6-methyl-4-oxo- -6,7,8,9-tetrahydro-pyrido(1,2-a)pyrimidine-3-carboxilate with isocyanates

The 9-carbamoyl derivatives /$\text{3}$–$\text{9}$/ can be prepared from title compound /$\text{1}$/ with isocyanates /$\text{2}$/. $\text{3}$–$\text{9}$ are mixtures of the cis /Z/ and trans /E/ imines and the enamine /e/. The equilibrium depends on the substituents R,X and on the solvent.     

Ein neuer Strukturtyp mit flächenverknüpften BaO6-Oktaedern: Ba6Nd2Al4O15

Summary A compound Ba₆Nd₂Al₄O₁₅ with a new structure-type was prepared by solid state reaction. It crystallizes with hexagonal symmetry, space group C _6v ⁴ – P 6₃mc;a=11.5696;c=6.9662 Å;z=2. Ba₆Nd₂Al₄O₁₅ has a dominating Ba/O-framework with incorporated AlO₆-octahedra and AlO₄-tetrahedra. A main feature of the structure are face connected BaO₆-octahedra. One of the point positions of the heavy atoms is occupied statistically by Ba²⁺ and Nd³⁺.