Gold catalysis: on the phenol synthesis.

[reaction--see text] For the gold-catalyzed phenol synthesis an intramolecular migration of the oxygen atom was proven. Several other late transition metals with d(8) configuration allow this conversion, providing evidence for Au(III) being a catalytically active species. On the other hand gold was still the most active catalyst and gives the cleanest conversion. With additional alkynyl substituents another ring could be closed to provide doubly annellated arenes.

Two isomorphous benzenesulfonamide crystal structures determined by intermolecular C-H...O, C-H...pi and C-H...Cl interactions.

The title compounds, N-[5-(4-chlorophenyl)furan-2-ylmethyl]-4-methyl-N-(prop-2-ynyl)benzenesulfonamide, (Ia), and N-[5-(2-chlorophenyl)furan-2-ylmethyl]-4-methyl-N-(prop-2-ynyl)benzenesulfonamide, (Ib), both C(21)H(18)ClNO(3)S, have isomorphous crystal structures. The crystal packing is mainly determined by intermolecular C-H...O and C-H...pi interactions. These interactions are very similar in (Ia) and (Ib). Additional intermolecular C-H...Cl interactions appear less important and are different in (Ia) and (Ib). The different positions of the Cl atoms result in small variations of the crystal packing of the two compounds.

Electronic communication in oligometallic complexes with ferrocene-based tris(1-pyrazolyl)borate ligands.

Ferrocene-based tris(1-pyrazolyl)borate ligands 1R-Li and 1R-Tl have been synthesized and used to generate a variety of heterotrinuclear transition metal complexes, 3R-M [R = H, SiMe(3), cyclohexyl, (cyclohexyl)methyl, phenyl; M(II) = Mn, Fe, Co, Ni, Cu, Zn]. The poor solubility of 3H-M is greatly enhanced by the introduction of large organic substituents into the 4-positions of all pyrazolyl rings. The unsubstituted ligand 1H-Li and the trinuclear complex 3Cym-Cu [Cym = (cyclohexyl)methyl] have been investigated by X-ray crystallography. 1H-Li, which represents the first example of a structurally characterized lithium tris(1-pyrazolyl)borate, forms centrosymmetric dimers in the solid state. A severe Jahn-Teller distortion was observed for the (Bpz(3))(2)Cu fragment in 3Cym-Cu. Compared to the parent compounds [(HBpz(3))(2)M], the presence of uncharged ferrocenyl substituents in 3R-M tends to shift the M(2+)/M(3+) redox potential to significantly more cathodic values. The opposite is true if the ferrocenyl fragments are in their cationic state, which results in an anodic shift of the M(2+)/M(3+) transition. Most interestingly, the two ferrocenyl fragments in 3R-Cu appear to be electronically communicating.

Pseudosymmetry and phase transition in dimethyl 2,3-bis(tricyclo.

The crystal structure of the title compound, C(26)H(34)O(4), shows a reversible phase transition at about 178 K. The structure of the high-temperature phase contains two independent molecules related by pseudosymmetry elements. Cooling through the phase-transition temperature results in a doubling of the c axis. The low-temperature structure contains four independent molecules related by pseudosymmetry elements. The phase transition results in a rearrangement of some weak intermolecular C-H.O interactions. The number of very weak C-H.O interactions, with H.O distances between 2.8 and 2.9 A, is increased in the low-temperature structure.

Dimethyl dispiro[tricyclo[3.3.1.1(3,7)]-decane-1,2'-bicyclo[1.1.0]butane-4',1"-tricyclo[3.3.1.1(3,7)]decane-1',3'-dicarboxylate, a strain-enhanced bicyclo[1.1.0]butane with a very short intramolecular C--H...H--C contact.

The title molecule, C(26)H(34)O(4), shows a very short repulsive intramolecular C-H.H-C contact, with an H.H distance of only 1.71 A. The flap angle varphi of the bicyclo[1.1.0]butane group is widened to 131.23 (8) degrees. Both methylene C atoms show tilt angles of 6.1 degrees. Bond lengths in the fused cyclopropane rings range from 1.501 (1) to 1.542 (1) A and are influenced by pi interactions with the carboxylate substituents.

Planar chirality: cycloaddition and transannular reactions of optically active azoninones that contain (E)-olefins.

Unsaturated nine-membered ring lactams that contain (E)-olefins within the ring are characterized by planar chiral properties. Thus, selective conversions of the double bond allowed a complete transfer of the planar chiral information into new stereogenic centers The basis of the transformations was the high activation barrier that prevented efficient flipping of the double bond at room temperature (epimerization pR <=> pS) with respect to the ring. Cycloadditions led diastereoselectively to cyclopropano, epimino, epoxy, and dihydroxy azonanones under mild conditions with moderately high yields. The epoxy azonanones were subjected to regio- and diastereoselective transannular epoxide opening/ring contraction sequences to give hydroxy indolizidinones. The regiochemical and stereochemical outcome strongly depends on the configuration of the oxirane and the chiral information of the lactam unit. The so-formed optically active bicycles with defined substitution patterns should serve as versatile building blocks in alkaloid synthesis.

Diastereo- and enantioselective synthesis of alpha,beta-disubstituted gamma-nitro methyl sulfonates.

A novel asymmetric synthesis of highly enantioenriched homotaurine precursors has been developed via diastereo-selective Michael addition of lithiated enantiopure sulfonates to nitroalkenes by using 1,2:5,6-di-O-isopropylidene-alpha-D-allofuranose as chiral auxiliary.

Solid-state transformation of 4, 2'-anhydro-5-(beta-D-arabinofuranosyl)uracil dihydrate to 4, 2'-anhydro-5-(beta-D-arabinofuranosyl)uracil monohydrate.

Crystals of 4,2'-anhydro-5-(beta-D-arabinofuranosyl)uracil, (I), obtained from an aqueous solution, were characterized as the dihydrate, C(9)H(10)N(2)O(5).2H(2)O, (Ia). In air, these crystals slowly transform to the monohydrate, C(9)H(10)N(2)O(5).H(2)O, (Ib), but remain crystalline. The solid-state transformation proceeds with the loss of one water molecule and a rearrangement of hydrogen-bonded layers of molecules. The furanose ring in (I) has an approximate C4'-exo,O4'-endo twist conformation. The central five-membered ring is slightly puckered. The uracil group is planar within experimental uncertainty.

Fluorescence studies and semiempirical calculations on alkali ion indicators.

Two newly synthesized cryptands act as sensitive Na(+)- and K(+)-selective indicators for cation concentrations above 20 µM. The fluorescence properties change markedly upon cation binding. In addition, the free ligands exhibit a pronounced sensitivity to pH, which is considerably lower for the cation complexes. Time resolved fluorescence is characterized by a decay time of about 5 ns that is attributed to the diprotonated protolytic state of the uncomplexed ligands. Semiempirical calculations show the systematic influence of the nitrogen lone pairs or the N-H bond on the stability of the system. The cause of the strong fluorescence intensity increase observed upon protonation of the fluorescent cryptands may be attributed to an increase in the S1-T x energy gap as a consequence of bridgehead nitrogen protonation.

Conformational analysis of cyclic peptides in solution.

The strategy and tactics of conformational analysis of cyclic peptides in solution is demonstrated by the example of cyclo(-D-Pro-Phe-Thr-Phe-Trp-Phe-). Spin-locked experiments like rotating frame nuclear Overhauser enhancement spectroscopy (ROESY), ROTO, and TOCSY are successfully applied to assign all proton signals and to obtain distance information. A crude conformational model was built using the nmr data. This starting model was refined by restrained molecular dynamics (MD) calculations using ROE derived distances and fixed bond angles as determined from homo- and heteronuclear coupling constants. To mimic the solvent and to reduce artifacts in an in vacuo calculation the charges of the solvent-exposed NH protons were gradually reduced according to the temperature gradients. The thus obtained "conformation" (mean of a 40 ps MD trajectory) shows very close similarity to x-ray structures in an orthorhombic and in two monoclinic crystal modifications of the same compound. The main difference is the breaking of an intermolecular hydrogen bond of the threonine hydroxyl group on dissolution of the crystal and forming an intramolecular hydrogen bond in solution.