Structure and biological activity of cationic [PtLCl(DMSO)]NO(3).DMSO complex containing a chelated diaminosugar: methyl-3,4-diamino-2,3,4,6-tetradeoxy-alpha-L-lyxopyranoside

Cationic platinum(II) complex [Pt(C(7)H(16)N(2)O(2))(DMSO)Cl]NO(3).DMSO containing one chloride anion, methyl-3,4-diamino-2,3,4,6-tetradeoxy-alpha-L-lyxopyranoside (C(7)H(16)N(2)O(2)) and dimethylsulfoxide (DMSO) molecules forming a square-plane has been prepared and characterised, both spectroscopically and by single-crystal X-ray diffraction. Biological tests performed using leukemia L1210 cells have shown that toxicity of the title complex is similar to that of cisplatin.

An assisted solvolysis of 23-spirostanyl bromides and tosylates. A new rearrangement of spirostanes to the bisfuran systems

Steroidal sapogenins bearing a good leaving group at C23 undergo a completely stereospecific rearrangement under a variety of conditions via a mechanism involving neighboring-group participation by the acetal oxygen atom in the departure of the nucleofuge from C23. The reactions of equatorial (23S)-23-bromo- or (23S)-23-tosyloxyspirostanes with either the alpha (25R) or beta (25S) oriented 25-methyl group lead to the bisfuran products with inversion of configuration at C23. The reactions of the starting compounds with axial substituents (23R) at C23 require drastic conditions and result in the formation of the corresponding olefin accompanied by the rearranged product (in the case of the 25S isomer only).

Reactions of hydroxymesitylboranes with metal alkyls: an approach to new sterically hindered (metaloxy)mesitylboranes

Reactions of mesitylboronic acid with alkyl derivatives of aluminum R(3)Al (R = Me, Et, Bu(i)), gallium (Me(3)Ga), and zinc (Et(2)Zn) were investigated. The treatment of mesitylboronic acid, MesB(OH)(2), with trimethylgallium afforded the discrete dimer [mu-(MesB(OH)O)GaMe(2)](2) (1), which is the simple example of a O-metalated boronic acid with no hydrogen bonding in the crystal lattice. In addition, the reaction of dimesitylborinic acid, Mes(2)BOH, with diethylzinc produced the low-valent zinc compound [(mu-Mes(2)BO)ZnEt](2) (2), which was also characterized by X-ray diffraction.

Diverse reactivity of dialkylaluminum dimesitylboryloxides [(mu-Mes2BO)AlR2]2. Synthetic and structural study

Several stable dimeric dialkylaluminum boryloxides of the formula [(mu-Mes2BO)AlR2]2 (R = Me (1), Et (2), iBu) have been prepared from dimesitylborinic acid Mes2BOH and trialkylaluminums R3Al. Compound 1 has been characterized by X-ray diffraction. These compounds exhibit diverse reactivity toward protonolytic reagents depending on the bulkiness of these reagents. Treatment of 1 with tert-butyl alcohol afforded crystalline species trans-[mu-tBuO)(Mes2BO)AlMe]2 (3), which is the first example of a mixed system containing boryloxide and alkoxide ligands together. Most surprisingly, Mes2BOH was found to undergo catalytic decomposition in the presence of [(mu-Mes2BO)AlR2]2 via the unexpected cleavage of one boron-carbon bond. The molecular structure of the decomposition product, i.e., trimesitylboroxin [MesBO]3 (4) is reported.

Crystal and Molecular Structure of N-(3,5-Dichloro-2-hydroxybenzylidene)- and N-(2-Hydroxy-3-methoxybenzylidene)aniline Oxides. Delocalisation in the Spacer of the Intramolecular H-Bond and the Problem of Quasi-Aromaticity

The hydrogen bond in the title compounds and their analogues with the spacer built of six heavy atoms (O,N,C,C,C,O) between the H-donor OH group and H-acceptor oxygen atom in the oxide group is much stronger than in the case of spacers with five heavy atoms. In spite of that, the delocalisation in the spacer does not depend on the strength of the H-bond, leading to the conclusion that quasi-aromaticity is not a proper term for these kinds of pseudorings. This is supported by analysis of the geometry of N-(3,5-dichloro-2-hydroxybenzylidene)- and N-(2-hydroxy-3-methoxybenzylidene)aniline oxides presented in this study and molecular geometries of five well solved structures retrieved from the CSD. Schleyer's index of aromaticity, NICS, is positive (i.e. indicating nonaromatic behaviour) for a model approximating the title H-bond system spacer indicating no ring current in the pseudoring whereas Li+-chelated system exhibits a slightly aromatic property (NICS < 0).