Triangular 30- and 27-membered hexaiminomacrocycles 4 and 5 of D(3) and C(3) symmetry, respectively, are readily obtained by unprecedented [3 + 3] cyclocondensation of (R,R)-1, 2-diaminocyclohexane with, accordingly, terephthalaldehyde and isophthalaldehyde. The course of the reaction, leading to macrocyclization, is governed by conformational constraints imposed on the structural components of the intermediate products, as shown by molecular modeling. X-ray analysis of cocrystal 4.AcOEt revealed that the macrocycle symmetry significantly departs from ideal D(3) symmetry due to crystal environment. Cyclic hexaamines 6 and 7 were prepared by sodium borohydride reduction of 4 and 5, respectively.

Simple circular dichroic method for the determination of absolute configuration of 5-substituted 2(5H)-furanones Gawronski, J.K.; van Oeveren, A.; van der Deen, H.; Leung, C.W; Feringa, B.L.

Scheme 6. Diastereoselective Additions of Me 3 SiCN (1) to N-Protected Amino Aldehydes 84 Scheme 7. Enantioselective Conjugate Additions of Me 3 SiCN (1) 85 Scheme 8. Regioselective Additions of Me 3 SiCN (1) to Enone 32 86 Scheme 9. Three-Component Silylative Strecker Reaction (a) and Strecker-Type Cyanosilylation of Imines (b) as the Routes to Silylated r-Aminonitriles Scheme 10. Unexpected Course of Addition of Me 3 SiCN (1) to N-Sulfinylimine 35 105

An exceptionally large size cuboctahedral imine cage is obtained from small size organic molecules in a thermodynamically driven [8+12] cyclocondensation. This is a demonstration of the role of entropy of symmetry as a driving force in reversible reactions.

Trianglamines, macrocyclic heteraphanes, were readily synthesised through a [3+3] cyclocondensation of (R,R)-1,2-diaminocyclohexane with terephthalaldehyde, followed by NaBH4 reduction and N-alkylation. The macrocyclic ring shows a remarkable ability to change its conformation, as a consequence of rotation about the C-N bonds or nitrogen inversion due to protonation or N-alkylation, as revealed by circular dichroism spectra, computational modelling and X-ray diffraction analysis. The flexible natures of the trianglamine macrocycles allow ready accommodation of a variety of guest molecules to form crystalline inclusion complexes of highly diversified interpenetrating structures.

The absolute configurations of 2-cyclohexenone cis-diol metabolites resulting from the biotransformation of the corresponding phenols have been determined by comparison of their experimental and calculated circular dichroism spectra (TDDFT at the PCM/B2LYP/Aug-cc-pVTZ level), optical rotations (calculated at the PCM/B3LYP/Aug-cc-pVTZ level) and by stereochemical correlation. It is found that circular dichroism spectra and optical rotations of 2-cyclohexenone derivatives are strongly dependent on the ring conformation (M or P sofa S(5) or half-chair), enone non-planarity and the nature and positions of the hydroxy and alkyl substituents. The effect of non-planarity of the enone chromophore, including the distortion of the C=C bond, is determined for the model structures by TDDFT calculations at the PCM/B2LYP/6-311++G(2d,2p) level. Non-planarity of the C=C bond in the enone chromophore is commonly encountered in 2-cyclohexenone derivatives and it is a source of significant rotatory strength contribution to the electronic circular dichroism spectra. It is shown that the two lowest-energy transitions in acrolein and 2-cyclohexenone and its derivatives are n(C=O)-π(C=O)* and π(C=C)-π(C=O)*, as expected, while the shorter-wavelength (below 200 nm) transitions are of more complex nature. In 2-cyclohexenone and its alkyl derivatives it is predominantly a mixture of π(C=C)-π(C=C)* and π(C=C)-σ* transitions, whereas the presence of hydroxy substituent results in a dominant contribution due to the n(OH)-π(C=O)* transition. A generalized model for correlation of the CD spectra of 2-cyclohexenones with their structures is presented.

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Absolute configurations and conformations of selected cis-1,2-dihydrodiols, isolated from bacterial enzyme-catalyzed arene dihydroxylation, have been examined by comparison of experimental and DFT-calculated CD spectra and confrontation with the results of X-ray diffraction studies in the crystalline phase. The equilibrium between the diene P and M conformers in cis-dihydrodiols is strongly dependent on the intramolecular OH-OH, OH-pi, and OH-F hydrogen bonding pattern and is crucial in determining the sign and magnitude of the long-wavelength diene pi-pi transition Cotton effect. The differences originate from a dominant contribution of either P-helical (1b, X=Me) or M-helical conformers (1d, X=F), or are due to M and P low-energy conformers, both contributing a positive rotational strength (1c, X=Br). Computations show that cis-dihydrodiol 1e (X=CF3) has only one M conformer stabilized by an intramolecular O-H...F hydrogen bond. cis-Dihydrodiol 1f (X=CN) shows a Cotton effect of the sign opposite to the sense of helicity of the dominating conformer. The results of the computations highlight the inadequacy of the Diene Helicity Rule and the Allylic Chirality Rule to correlate observed Cotton effects with dihydrodiol absolute configuration. A reliable model is presented to predict the absolute configuration of substituted benzene dihydrodiol derivatives from CD spectra, based on the confrontation of DFT-computed and experimental CD spectra. For 3-alkyl derivatives, a simple noncomputational model is offered, which is based on the contributions of the allylic hydroxy groups and the diene core in P and M conformers.