Spectroscopy and photophysics of bifunctional proton donor-acceptor indole derivatives.

We report spectroscopic and photophysical studies of a series of selected indole derivatives in solutions and under supersonic jet isolation conditions. All the compounds can assume two rotameric forms, syn and anti. The bifunctional molecules containing both the hydrogen bond donor (indole NH group) and acceptor centers (oxygen, nitrogen, or sulfur atoms) located in separate moieties covalently linked by a single bond are compared with the compound that does not have any acceptor center, 2-(1H-pyrrol-2'-yl)-1H-indole. The former compounds (containing furan, thiazole, or thiophene moieties) were anticipated to show solvent-dependent photophysics. Contrary to the expectations, all the compounds reveal very efficient fluorescence, independent of solvent polarity and hydrogen bond donor and acceptor abilities. Laser spectroscopic studies combined with supersonic jet techniques and quantum chemical computations have been performed in order to identify the rotameric forms and to gain insight into the changes in the molecular structure accompanying electronic excitation.

Tosyl esters of cinchonidine and cinchonine alkaloids: the structure-reactivity relationship in the hydrolysis to 9-epibases.

In the crystal structures of the diastereoisomers of O-tosylcinchonidine [(9R)-cinchon-9-yl 4-methylbenzenesulfonate], (I), and O-tosylcinchonine [(9S)-cinchon-9-yl 4-methylbenzenesulfonate], (II), both C(26)H(28)N(2)O(3)S, both molecules are in an anti-closed conformation and, in each case, the position of the aryl ring of the tosylate system is influenced by an intramolecular C-H···O hydrogen bond. The molecular packing in (I) is influenced by weak intermolecular C-H···O and C-H···π interactions. The crystal structure of (II) features C-H···π interactions and van der Waals forces only. The computational investigations using RHF/6-31G** ab initio and AM1 semi-empirical methods performed for (I) and (II) and their protonated species show that the conformational and energetic parameters of the molecules are correlated with differences in their reactivity in hydrolysis to the corresponding 9-epibases.

5,6,7,8-Tetra-hydro-quinolin-8-one.

In the quinoline fused-ring system of the title compound, C(9)H(9)NO, the pyridine ring is planar to within 0.011 (3) Å, while the partially saturated cyclo-hexene ring adopts a sofa conformation with an asymmetry parameter ΔC(s)(C6) = 1.5 (4)°. There are no classical hydrogen bonds in the crystal structure. Mol-ecules form mol-ecular layers parallel to (100) with a distance between the layers of a/2 = 3.468 Å.

5,6,7,8-Tetra-hydro-quinoline 1-oxide hemihydrate.

In the title compound, C(9)H(11)NO·0.5H(2)O, the asymmetric unit contains two similar mol-ecules of 5,6,7,8-tetra-hydro-quinoline 1-oxide and one water mol-ecule. The water mol-ecule links the two O atoms of both independent N-oxides into dimers via O-H⋯O hydrogen bonds, forming a three-dimensional network along [101], which is additionally stabilized by weak C-H⋯O inter-molecular inter-actions. In each mol-ecule, the saturated six-membered rings exist in a conformation inter-mediate between a half-chair and sofa.

A new approach to difficult Fischer synthesis: the use of zinc chloride catalyst in triethylene glycol under controlled microwave irradiation.

[reaction: see text]. Application of triethylene glycol with catalytic quantity of zinc chloride (ZnCl2/TEG) is described as a new and efficient reaction medium for a difficult Fischer synthesis, leading to sensitive indoles. Transformation of the 3-acetyl-1-methylthiocycloalka[c]pyridine phenylhydrazones and p-methoxyphenylhydrazones into the 2-(2-pyridyl)indoles and 5-methoxy-2-(2-pyridyl)indoles, which are the synthons in our total synthesis of the sempervirine-type alkaloids, is carried out under controlled microwave irradiation in dry zinc chloride solution (0.16 M) in TEG. This protocol produces indoles from acetophenone or cyclohexanone via their phenylhydrazones in excellent yields.