Petr Holý

Axially chiral dilactams. Synthesis, racemization barriers and crystal structures

Abstract The racemic as well as optically active dilactams 1 and 2 were prepared as the first representatives of axially chiral dilactams possessing a biaryl axis as the sole element of chirality. Their absolute configurations and inversion barriers were determined. The molecular structure and supramolecular self-assembly of the racemic dilactams directed by hydrogen bonding and aryl–aryl stacking was elucidated by single crystal diffraction analysis.

Self-assembly of chiral hydrogen-bonded grid layers from terephthalic Siamese twins

Abstract 2,2′,5,5′-Tetracarboxy- and 2,2′,5,5′-tetracarbamoyl-substituted biphenyls and also the 2,2′,3,3′,6,6′-hexacarboxy-substituted analogue behave as Siamese twins of terephthalic tectons in the single crystal self-assembly, giving rise to chiral 2D grid layers. A comparison has been made with the corresponding 2,2′,6,6′-tetrasubstituted biphenyls which mimic isophthalic twins in their self-assembly.

Self-assembly of enantiopure and racemic 2,2′,6,6′-tetrasubstituted biaryl tectons into hydrogen bonded chiral squares and infinite chiral square layers

Abstract Both chiral and achiral hydrogen bonding o-,o-,o′-,o′-tetrasubstituted biaryls often exhibit unique self-assembling properties giving rise to chiral square cyclotetramers. The individual chiral squares self-assemble further with the formation of infinite layers which are either achiral or are chiral (homochiral). A priori analysis reveals various hydrogen bonding modes which may take part in the self-assembly, differing each from the other by structure and symmetry of the resulting squares and layers. Results of the theoretical analysis are compared with the experimental findings obtained from X-ray crystallographic analysis of three novel and two already known isosteric biaryl tectons, (S)-2a, (RS)-2a, 3a, (S)-5 and (RS)-5, respectively.

α-Amino acids and dioxopiperazines crowned at the α-carbons with polyether macrorings. Synthesis, complexation and self-assembling properties

Abstract Crowned α-amino acids 7a–c and their dioxopiperazine derivatives 12a–c were prepared from the easily accessible masked tris(hydroxymethyl)aminomethane 1 . X-Ray crystal structures of the free as well as alkali metal ion coordinated compounds were investigated.

Solvent and leaving group effects on the mono- vs. Dialkylation of alkali salts of diethyl malonate with 1,2-bis-, 1,2,4,5-tetrakis- and 1,2,3,4,5,6-hexakis-(Halomethyl)benzenes. A new insight into selectivity control of malonester synthesis

Contrary to the widely held opinion that protic (“acidic”) solvents favor monoalkylation whereas aprotic (“inert”) solvents support dialkylation of diethyl malonate carbanion, exactly opposite results have been obtained in the reaction of the dibromide 7, tetrabromide 4 and hexabromide 1 in ethanol and dimethyl sulfoxide, the former solvent preferring strongly dialkylation (cyclization) and the latter monoalkylation. Investigation in a broader spectrum of solvents demonstrated that hydrogen bonding as well as ion-pairing may play an important role in the selectivity control, both strongly supporting dialkylation. When a separation of ion-pairs is induced with 18-crown-6, monoalkylation prevails in the reaction. The solvent and the leaving group employed have been found to participate in the selectivity control. In DMSO, propensity to dialkylation increases strongly in the order I<Br⪡Cl, again in discord with earlier predictions. Rationale for the novel findings is provided on the basis of kinetic analysis of the overall reaction and is expressed by the limiting equations (5) and (7).

C-C Coupling reaction of 1,5-dibromo-2,6-dihydroxynaphthalene with alkali 2-naphthoxide. Opposite effects of counterion coordination and hydrogen bonding on stereoselectivity in the formation of cis- and trans-1,1′:5′,1″-ternaphthyls

Abstract The title reaction yields cis- and trans-2,2′,6′,2″-tetrahydroxy-1,1′:5′,1″-ternaphthyls as the main products. In contrast to non-selective distribution of the stereoisomers in the thermodynamic equilibrium, very high selectivity can be attained under conditions of kinetic control. The observed values of cis-/trans- ratios range between the extremes 94:6 and 6:94, depending on the solvent and counterion employed. The coordination of the metal counterion plays a key role in the reaction performed in toluene, supporting formation of the cis-stereoisomer. When the coordination ability of the counterion is supressed by 18-crown-6, intramolecular hydrogen bonding of the departing bromide group prevails in the stereocontrol, providing support for the trans-stereoisomer formation.

A NOVEL ONE-POT CONVERSION OF 2-NAPHTHOLS INTO 1,1'-BINAPHTHALENE-2,2'-DIOLS

Abstract A simple two-step, one-pot procedure based on the treatment of sodium 2-naphthoxide with bromine yields 1,1′-binaphthalene-2,2′-diol in a high yield and an excellent purity. The procedure is applicable also to preparation of the symmetrically disubstituted analogues.

Helix-forming self-assembly of enantiopure 2,2′-dimethylbiphenyl-6,6′-dipropiolic acid and amide organized by hydrogen bonds

Abstract Single-crystal X-ray diffraction revealed that the molecules of both the title compounds ( S )- 5 and ( S )- 6 are linked, via double hydrogen bonds, in infinite chains which follow the crystallographic symmetry of the three- and four-fold screw axis, respectively. To our knowledge this represents the first documented case when intermolecular carboxylic hydrogen bond constitutes an integral part of a helix backbone set up from repeating homochiral subunits.

Macrocyclic cis- and trans-bis(α-amino acids) and their intraannular Cu(II) complexes. Conformational in–out dichotomy and crystal packing

Abstract Macrocyclic bis(α-amino acids) cis - and trans - 2a - b were prepared from the selectively protected tris(hydroxymethyl)aminomethane 3 . The X-ray structures of the free bis(amino acids) and/or of the corresponding Cu(II) complexes have been determined allowing an unambiguous configurational assessment. At the same time, conformational in – out dichotomy of the functional groups has been demonstrated in the bis(amino acids) as well as in their Cu(II) complexes.