Self-complementary

Three [3]catenanes with cavities large enough to accommodate aromatic guests have been designed and synthesized (yields = 5-20 %) by means of kinetically controlled self-assembly processes. The X-ray structural analysis of one of three [3]catenanes confirmed the presence of a rectangular cavity (dimensions = 7 x 11 A) lined by pi-electron-rich recognition sites and hydrogen-bond acceptor groups. In spite of their apparently ideal recognition features, none of these [3]catenanes bind guests incorporating a pi-electron-deficient bipyridinium unit. However, the template-directed syntheses of the [3]catenanes also produce, in yields of 2-23%, [2]catenanes incorporating a 1,5-dioxynaphtho[38]crown-10 interlocked with a bipyridinium-based tetracationic cyclophane. The X-ray structural analyses of two of these [2]catenanes revealed that a combination of [pi...pi] and [C-H...pi] interactions is responsible for the formation of supramolecular homodimers in the solid state. 1H NMR spectroscopic investigations of the four [2]catenanes demonstrated that supramolecular homodimers are also formed (Ka= 17-31M(-1), T= 185 K) in (CD3)2CO solutions. Dynamic 1H NMR spectroscopy revealed that the 1,5-dioxynaphtho[38]crown-10 and tetracationic cyclophane components in the four [2]catenanes and in the three [3]catenanes circumrotate (deltaGc(not equal to) = 9-14 kcal mol(-1)) through each other's cavity in (CD3)2CO. Similarly, the 1,5-dioxynaphthalene and the bipyridinium ring systems rotate (deltaGc(not equal to) =10-14 kcal mol(-1)) about their [O...O] and [N...N] axes, respectively, in solution.     

SEASONAL TRENDS IN ERYTHEMAL and CARCINOGENIC ULTRAVIOLET RADIATION AT MID-SOUTHERN LATITUDES1989–1991

A network of solar carcinogenic/erythemal ultraviolet radiometers has been established in New Zealand. Daily integrated irradiances of this biologically harmful ultraviolet radiation for 1989, 1990 and 1991 are reported from radiometers located at Wellington (41°S) and Christchurch (43.5°S) and for 1990 and 1991 from the Auckland (37°S) radiometer. Although the monitoring program has not been running sufficiently long to discern any long-term changes in levels of solar ultraviolet radiation, shorter term trends are apparent, which are attributed to a seasonal cycle in levels of ozone at midlatitudes and changes in atmospheric aerosols.     

Direct conversion of macrocyclic furans into macrocyclic isothiazoles

The first calixhetarenes with more than one heteroatom in the constituent rings are prepared in one step by treatment of calix[4]furan 1a and calix[6]furan 1b with ethyl carbamate, thionyl chloride and pyridine to give 2, 3, 4 and 5, 6, 7 respectively; these products have been characterised by X-ray crystallography which reveals that in 2 all eight heteroatoms lie on one face of the macrocyle.     

Structural Consequences of S → Se Substitution in some Symmetrical [M(S2CNR2)3] Complexes

The consequences of replacement of the symmetrically chelate ligands in [M(E₂CNR₂)₃] (E = S, Se) complexes of potential 32 symmetry by analogous mixed S,Se unsymmetrical chelates are explored for both small (M = Co) and large (M = In) metal atoms, and R = primary (Et) and secondary (ⁱPr) alkyl substituents by way of low‐temperature single crystal X‐ray studies of [(Co(SSeCNEt₂)₃] ([Co(Se₂CNEt₂)₃] also determined as datum), and [In(SSeCNR₂)₃], R = Et, ⁱPr. The structure of [(ⁱPr₂N·CS·Se)₂] is also recorded.     

A finite-difference solution of the Hartree–Fock equations for diatomic molecules

A more general application of the self-consistent field iteration is coupled with a finite-difference Newton–Raphson algorithm to solve the set of coupled second-order integro-differential equations with split boundary conditions which constitutes the Hartree–Fock problem for diatomic molecules. The N orbitals are assumed to be of the form ψ_α = L_α(λ) M_α (μ)e^imα^? (2π)^?1/2, (α = 1, …?, N), where λ, μ, and ? are the usual confocal elliptical coordinates. Requiring the expectation value of the electronic Hamiltonian to be stationary with respect to independent variations of the functions L_α and M_α, subject to constraints of orthonormality, leads to a set of coupled one-dimensional differential equations for the functions L_α and M_α. In the new method a corresponding set of finite-difference equations including the split boundary conditions for each function, as well as the Lagrange multipliers and associated constraints on normalization and orthogonality, are incorporated into a large system of nonlinear algebraic equations which is solved by means of a coupled self-consistent field-generalized Newton–Raphson iteration. As examples, calculations of the (1)^{2 1}Σ and (1) (2pσ_u) ³Σ states of H₂ are presented. The calculated energy for the ¹Σ state of H₂ is 99.985% of the three-dimensional Hartree–Fock limit. The discrepancy is due to the assumed factored form of the orbitals ψ_α, and a generalization of the finite-difference method is suggested to improve the results.     

Convenient Asymmetric Syntheses of anti-beta-Amino Alcohols

Condensation of allylborane reagents 9 and 12 with aldehydes gave anti-3-[(diphenylmethylene)amino]-1-alken-4-ols 10 and 13 with high relative and absolute stereocontrol. Subsequent deprotection gave the corresponding free anti-3-amino-1-alken-4-ols 11 and 14. Alternatively, reaction of imines 13a, 13f, and 13g with trifluoromethanesulfonic anhydride and acidic methanol gave, via rearrangement, double inversion, and hydrolysis, the isomeric anti-4-amino-1-alken-3-ols 22, 38a, and 38b in good yield. The stereochemistry of the rearrangement products has been established by a single crystal X-ray study of compound 37 and by chemical correlation.     

Synthesis of monofluorinated 1-(naphthalen-1-yl)piperazines

A series of regioisomerically monofluorinated 1-(naphthalen-1-yl)piperazines is described.     

Micelle studies using a metal ion/murexide indicator system

Summary Complex formation between divalent metal ions and the hydrophilic murexide anion in the presence of anionic micelles has been employed to study aspects of micelle formation, the binding of divalent metal ions to micelles, and the kinetics of metal-complex formation in the presence of micelles.

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Zusammenfassung Die Komplexbildung zweiwertiger Metallionen mit dem hydrophilen Indikator Murexid wurde in Gegenwart anionischer Mizellen untersucht. Die Indikatorreaktion wurde benutzt, um Aussagen über Mizellbildung, Bindung zweiwertiger Metallionen an Mizellen und die Kinetik der Metallkomplexbildung bei Anwesenheit von Mizellen zu erhalten.

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With 8 figures and 1 table

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Dedicated to Prof.G. Rehage on the occasion of his 60th birthday.     

Chemo-enzymatic synthesis of (−)-epipentenomycin I

A chemo-enzymatic synthesis of (−)-epipentenomycin I is reported using a lipase-catalysed kinetic resolution of the racemic pentacyclic alcohol 8. Flash vacuum pyroloysis of (−)-8 so obtained gave (−)-(4R)-4-hydroxy-5-methylene-2-cyclopentenone. Epoxidation of this compound with dimethyldioxirane followed by hydrolytic ring-opening of the resulting epoxide gave (−)-epipentenomycin I.     

Synthesis of titanium(IV) guanidinate complexes and the formation of titanium carbonitride via low-pressure chemical vapor deposition

The mono(guanidinato) complex [Ti(NMe2)2Cl{i-PrNC[N(SiMe3)2]N-i-Pr}] (1) was prepared by reaction of [Ti(NMe2)2Cl2] with 1 or 2 equiv of the lithium guanidinate salt [Li{i-PrNC[N(SiMe3)2]N-i-Pr}]. Compound 1 has been characterized by X-ray crystallography. Treatment of TiCl4 with 2 equiv of [Li{i-PrNC[N(SiMe3)2]N-i-Pr}] resulted in the formation of dark red crystals. X-ray crystallography showed that these crystals consist of a 70:30 mixture of two bis(guanidinato) complexes, namely, [TiCl2{i-PrNC[N(SiMe3)2]N-i-Pr}{i-PrNC(N=CMe2)N-i-Pr}] (2) and [TiCl2{i-PrNC[N(SiMe3)2]N-i-Pr}{i-PrNC[N(H)-i-Pr]N-i-Pr}] (3). Both compounds 2 and 3 possess a transformed guanidinate ligand. Low-pressure chemical vapor deposition of either compound 1 or [TiCl2{i-PrNC(NMe2)N-i-Pr}] (4) at 600 degrees C results in thin films of titanium carbonitride.