Intramolecular photocycloaddition of β-stilbazoles tethered by silyl chains

Intramolecular (2+2) photocycloaddition of β-stilbazoles tethered by silyl chains took place with high efficiency. Complexation with dicarboxylic acid or catechol further enhanced both the efficiency and stereoselectivity.     

Fluoroalkylation of aromatics: An intramolecular radical cyclization of 4-chloro-1,1,2,2,3,3,4,4-octafluorobutylbenzenes

In the presence of sodium dithionite and DMSO, the intramolecular radical cyclization of 4-chloro-1,1,2,2,3,3,4,4-octafluorobutylbenzenes is achieved to give the corresponding cyclic compounds in moderate to good yields.     

Temperature coefficient of NH chemical shifts of thioamides and amides in relation to structure

NH chemical shift temperature coefficients have been measured in a large series of N-substituted-3-piperidinethiopropionamides in which the NN distances are short but of varied length, as well as in a couple of the corresponding amides and in some simpler amides and thioamides. Geometries are calculated by means of ab initio DFT methods. The N-substituted-3-piperidinethiopropionamides show in most cases strong intramolecular N–HN hydrogen bonds according to IR spectra and ab initio calculations. For compounds with rather short NN distances the S=C–N–H moiety is non-planar. Dihedral angles as small as 160° are found. The NH chemical shift coefficients measured in non-polar solvents in all the N-substituted-3-piperidinethiopropionamides are more negative (−8 to −17 ppb/K) than in non-hydrogen bonded thioamides. For the latter in non-polar solvents like CDCl₃ and toluene the temperature coefficients are as small as −1 to −4 ppb/K. The large negative effects can be related not only to the non-planarity of the thioamide group in a way that the more pronounced the non-planarity the more negative the temperature coefficients, but also to strong hydrogen bonding and the fact that the acceptor is a nitrogen. For similar amides with non-planar amide groups and nitrogen acceptor large negative temperature coefficients are likewise seen. In polar solvents like DMF the effects in simple thioamides are uniform and close to −6 ppb/K, whereas in the more complex compound like 4p(t) the temperature coefficient is close to 0. An essential feature of measuring temperature coefficients of compounds without strong intramolecular hydrogen bonds in non-polar solvents and at low temperatures is to keep the concentration low enough to avoid dimerisation.     

Synthesis of latonduine derivatives via intramolecular Heck reaction

The synthesis of indole ring-fused benzazepinone series as latonduine derivatives has been developed via an intramolecular Heck reaction. The scope has been enlarged not only to indole moiety but also to pyrrolo and benzo[b]thiophene nuclei. Several derivatives prepared have been evaluated in vitro for their antiproliferative activities on breast cancer cell lines. Some of them showed promising cytotoxic activities.     

Heterogeneous intermolecular hydroamination of terminal alkynes with aromatic amines

Heterogeneous intermolecular hydroamination of alkynes with aromatic amines using inexpensive transition metal-exchanged clay catalysts was investigated. Reaction of terminal alkynes with aromatic amines gave higher yields of imines.     

Synthesis of a new tricyclic 3-(tetrazol-5-yl)pyridine system from 2-(azidomethyl)nicotinonitriles

2-Methyl-3-cyanopyridines were converted into the corresponding 2-azidomethyl derivatives, which then underwent an intramolecular cycloaddition reaction. A novel heterocyclic system containing a 3-(tetrazol-5-yl)pyridine unit was obtained in this way.     

The intramolecular hydrogen bond in ortho-hydroxy acetophenones

The crystal structures of two ortho-hydroxy ketones (5-chloro-2-hydroxyacetophenone (I K) and 3,5-dichloro-2-hydroxyacetophenone (II K)) have been determined with X-ray diffraction at 100 K. A comparison of steric effects on properties of pseudoaromatic hydrogen bonds in ortho-hydroxy acetophenone and ortho-hydroxy ketimines have been carried out with the application of crystallographic data.

Nuclear quadrupole resonance (NQR) spectra have been measured and interpreted.     

Application of the stabilization method to interacting resonances

The stabilization method is applied to the case of interacting resonances in the photo-dissociation of van der Waals clusters composed by a rare gas atom bound to a dihalogen molecule. The study of an illustrative two-dimensional model consisting in a T-shaped NeI₂ molecule shows the adequacy of the method whenever the projection of the stabilization wave functions on the assumed prepared initial state is accounted for. The agreement of the fragmentation cross-sections with some previous results using the effective resolvent method and accurate close-coupling calculations is excellent. The method reveals its utility as a complementary tool since allows, through the analysis of the stabilization wave function in terms of zero-order levels, a precise characterization of the resonant states involved. Received 5 April 2002 / Received in final form 24 May 2002 Published online 19 July 2002     

对称双吡咯甲烷的合成与分子内氢键的研究

５－甲基吡咯－２－羧酸酯在磺酰氢，溴或四乙酸铅作用下，生成相应的在５－甲基上含取代基的产物，后者不经分离不便可自缩合得标题化合物，核磁共振氢谱研究和分子构象木匠，当３，３位的取代基为甲酸（酯）基或乙酸（酯）基时，可形成３，３位酯基与另一吡咯环上的氮氢之间的分子内氢键，而３，３位是其它取代基，如乙酰基，丙酸（酯）基，丁酸（酯）基时不能形成类似的分子内氢键。     

Mannich bases as model compounds for intramolecular hydrogen bonding I. Solid state structures and molecular calculations

Summary A survey of the structures and the properties of the hydrogen bonds inortho-aminomethylphenols and -naphthols in the solid state is presented. The results are compared with molecular structure calculations. The solid state complexes can exist in the molecular or in zwitterionic form. In the last case, only intermolecular hydrogen bonds forming cyclic dimers or linear chains were detected.

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Mannich-Basen als Modelle für Intramolekulare Wasserstoffbrücken, 1. Mitt. Festkörperstrukturen und Molekülrechnungen

Zusammenfassung Eine Übersicht über Strukturen und Eigenschaften von Wasserstoffbrücken inortho-Aminomethylphenolen und -naphtholen wird präsentiert. Die Ergebnisse werden mit Molekülrechnungen verglichen. Im Festkörper existieren diese Verbindungen in neutraler oder in zwitterionischer Form. Für den zweiten Fall können nur intermolekulare Wasserstoffbrücken nachgewiesen werden, und zwar in Dimeren oder in linearen Ketten.