Tadeusz Połoński

Enantioselective Inclusion Complexation of N‐Nitrosopiperidines by Steroidal Bile Acids

N-nitrosamines, whose chirality is solely due to hindered rotation about the N-N bond, are enantioselectively enclathrated by the crystal host matrices of cholic or deoxycholic acid, as evidenced by X-ray crystallography (see structure in picture) and CD spectra.

Supramolecular structures formed by 2-aminopyridine derivatives.

A family of N,N′-bis(2-pyridyl)aryldiamines were prepared and their solid state structures investigated by X-ray crystallography. Due to a low energy barrier to C–N rotation, the 2-arylaminopyridine system can adopt either Z or E conformations, which may lead to conformational polymorphism. The E,E conformers form designated hydrogen-bonded polymeric tapes with the dimeric R22(8) motif. In contrast, the Z,Z conformers assemble via N–H⋯N hydrogen bonds, generating the catemer motif that leads to complex 1D, 2D or 3D supramolecular structures. The two types of intermolecular hydrogen-bonding motifs observed in the crystal structures can be easily differentiated with the assistance of solid state IR spectroscopy.

Absolute sense of twist of the benzil molecule in its enantiomorphous crystals and inclusion complexes with optically active hosts

Abstract The solid-state CD spectra were measured for optically active trigonal crystals of benzil (dibenzoyl) and its crystalline inclusion complexes with cholic and deoxycholic acids. The observed negative Cotton effect corresponding to the lowest energy n–π* transition was correlated with the P helicity of the strongly twisted α-diketone moiety. The absolute configuration of the enclathrated guest molecule in the 1:2 inclusion complex between benzil and cholic acid was also determined by X-ray crystal analysis.

Synthesis, stereochemistry, and chiroptical spectra of cyclopropyl lactones and thionolactones

Abstract Several optically active substituted 3-oxabicyclo[3.1.0]hexan-2-ones and their thiocarbonyl analogues were synthesized, and their circular dichroism spectra are reported. It was found that the n-π ∗ Cotton effect sign is determined by the helicity of an inherently chiral chromophore formed by the lactone or thiolactone group and the cyclopropyl moiety. The π-π ∗ Cotton effect of thiocarbonyl compounds shows opposite sign to that observed for the lowest energy transition. The crystal structures of two compounds were solved to establish their molecular geometries.

Conformational properties and chiroptical spectra of lactams and thiolactams with 2-azabicyclo[2.2.1]heptane, 2- and 3-azabicyclo[3.2.1]octane skeletons

Abstract The CD spectra of several bicyclic lactams and thiolactams were measured in different solvents. The concentration dependence of the spectra observed in hydrocarbon solvents was attributed to shifts in the equilibrium between monomer and hydrogen-bonded dimer forms. The CD of some compounds is characterized by unusually strong Cotton effects resulting from non-planarity of the amide bonds due to internal strain of the bicyclic skeletons. The X-ray crystallographic structures of 2a , c , 3b , d and 4a , b showed different degrees of distortion of the amide or thioamide moieties from planarity, which causes inherent chirality of the chromophores and profoundly affects the Cotton effect sign and magnitude. This distortion also restricts application of the sector rules for prediction of the n–π * CD sign, since they can be used only for compounds with planar chromophores.

Synthesis, structure and chiroptical spectra of the bicyclic α-diketones, imides and dithioimides related to santenone

Abstract Isomeric α-diketones, imides and dithioimides related to santenone were prepared in a multistep synthesis from (+)-camphor and their CD spectra compared with those of analogous chromophoric systems related to camphor. In the case of conformationally rigid α-diketones the methyl substituents at C-7, lying on the symmetry plane of the chromophore, exert only a weak contribution to the n–π* Cotton effects. In contrast, the Cotton effect magnitudes of the anhydrides, imides and dithioimides are significantly affected by the substituents at C-8. The steric interaction of these chromophores with the syn -methyl group at C-8, leading to the chromophore distortion, was confirmed by X-ray crystallographic studies.

Synthesis of optically active monothioimides with chirality due to sulphur substitution

Abstract Two optically active bicyclic monothioimides were prepared via chiral derivatives of cis -1,2-cyclopropanedicarboxylic and cis -1,3-cyclopentanedicarboxylic acids and their absolute configurations were assigned.

Chiroptical spectra of bicyclic selenolactams. Optical activity of the singlet–triplet transition

Abstract Two selenolactams with rigid 2-azabicyclo[2.2.1]heptane skeletons were prepared by reaction of the corresponding lactams with P 4 Se 10 . A comparison of their UV–vis and CD spectra with those of the carbonyl and thiocarbonyl analogues showed a similar character of the lowest-energy electronic transitions and the same signs of the corresponding Cotton effects. The MCD spectra of selenolactams revealed that their n–π* absorption band is dominated by the singlet–triplet component. A very weak CD corresponding to this component has an opposite sign to its much stronger singlet–singlet counterpart observed at the blue edge of the n–π* band.

Conformational properties, chiroptical spectra, and molecular self-assembly of 2,3-piperazinodiones and their dithiono analogues.

A family of chiral cyclic oxamides was prepared by the condensation of optically active 1,2-diamines with diethyl oxalate. Thionation of the products with Lawessons reagent afforded a series of chiral 2,3-piperazinedithiones. Molecular geometries of the title compounds were studied with the use of quantum mechanical DFT calculations and were compared to the X-ray crystallographic results. The heterocyclic six-membered ring adopted a half-chair conformation with the C-5 substituent preferably at the equatorial position, whereas a substitution at the nitrogen atoms resulted in domination of the axial form in the conformational equilibrium. The opposite helicity of the twisted oxamide chromophore in the axial and equatorial conformers led to the opposite signs of the Cotton effects corresponding to two pi-pi* electronic transitions. The CD signs can be predicted by a simple helicity rule. The same rule is valid for 2,3-piperazinodithiones, where a substitution of sulfur for oxygen in the carbonyl groups results in bathochromic shifts of the absorption and CD bands. The crystal packing analysis of several 2,3-piperazinodiones revealed that strong NH...O=C intermolecular hydrogen-bonding interactions generating the chain motif resulted in the formation of 3-D networks as well as with the use of the cyclic hydrogen-bond motif tape structures.

The 2:1 cocrystal of benzamide and pentafluorobenzoic acid

The crystal structure of the title compound, benzamide-2,3,4,5,6-pentafluorobenzoic .acid (2/1), 2C 7 H 7 NO·C 7 HF 5 O 2 , consists of centrosymmetric hexameric supermolecules composed of four amide and two carboxylic acid molecules connected via O-H···O and N-H···O hydrogen bonds. No phenyl-perfluorophenyl π-π stacking interactions are observed in this cocrystal.