Spectrophotometric analysis, thermal analysis and gravimetric determination of some metal ions with oxime and Schiff's base derivatives of N-furoylphenylhydroxylamine

The oxime and Schiff's base of N-furoylphenylhydroxylamine form complexes with Co²⁺, Cu²⁺, Zn²⁺ and Fe³⁺. These complexes were studied by means of the UV — Vis. spectra of nujol mulls, electron spin resonance (ESR) spectra and magnetic susceptibility to determine their stereochemistry. The complexes were characterized via elemental analyses, molar conductivities and thermogravimetric analyses. Organic reagents were used for the gravimetric determination of Co²⁺, Cu²⁺ and Fe³⁺ through the precipitation of their complexes. The compounds were also used for separation of a binary mixture of Cu²⁺ and Cu²⁺. Interferences were studied.     

Crystal Structure and Molecular Absolute Configuration of （＋）－Isocedranol （C_（15）H_（26）O）

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Substitution with retention in organoboranes and utilization of the phenomenon for a general synthesis of pure enantiomers

Organoboranes, readily available via the hydroboration of unsaturated organic compounds, exhibit a remarkable versatility in their reactions. The boron atom in these organoboranes can be readily converted into a wide variety of organic groups under very mild conditions, providing simple versatile syntheses of organic compounds. Exploration of these substitution reactions reveal that, with rare exceptions, the organoboranes transfer the alkyl group to other elements of synthetic interest with complete retention of stereochemistry. Recently we have discovered a method of synthesizing essentially optically pure organoborane intermediates. These optically active alkyl groups attached to boron can also be transferred with complete retention of optical activity. Consequently, it is now possible to achieve by a rational synthesis the preparation of almost any optically active compound with a chiral center, either R- or S-, in essentially 100% enantiomeric excess.     

A new method for the synthesis of CF3-containing aminovinyl ketones

A new method for the synthesis of aminovinyl trifluoromethyl ketones was developed. The method is based on the reactions of 4-sulfonyl-1,1,1-trifluorobut-3-ene-2,2-diols with various alkyl-, aryl-, dialkyl-, and alkylarylamines. The stereochemistry of the compounds obtained was studied.     

Absolute stereochemistries and total synthesis of (+)-arisugacins A and B, potent, orally bioactive and selective inhibitors of acetylcholinesterase

In the current studies, we used the Kakisawa-Kashman modification of the Mosher NMR method to determine the complete absolute stereochemistry of arisugacins. We also report the convergent total synthesis of (+)-arisugacins A and B by a sequence including (i) ruthenium complex-catalyzed asymmetric reduction of the cyclohexenone derivative; (ii) stereoselective construction of the arisugacin skeleton by a Knoevenagel-type reaction of an α,β-unsaturated aldehyde derivative with production of a 4-hydroxy-2-pyrone derivative as a key reaction; and (iii) stereoselective dihydroxylation to give the diol derivative, followed by deoxygenation. Accordingly, we defined the absolute structures of arisugacins A and B as 4a-(R),6a-(R),12a-(R), and 12b-(S). Finally, we characterized the bioactivities of the synthetic intermediates to understand the structure-activity relationships of the arisugacins.     

新型含吡啶基的不对称膦酸酯衍生物的合成与生物活性

通过2-氯-5-氯甲基吡啶与亚磷酸酯的Michaelis-Becker反应合成得到10个新型含吡啶基的不对称膦酸酯衍生物, 并对环状亚磷酸酯与2-氯-5-氯甲基吡啶反应的立体化学进行了研究, 结果表明: 不对称环状亚磷酸酯的电子效应和立体效应对反应的立体化学有着重要影响. 初步的生物活性结果表明, 该类化合物不具有杀虫活性, 但显现出较好的杀菌活性.     

Catalytic phosphorylation of polyfluoroalkanols. 17. Synthesis and the stereochemistry of tris(α-trifluoromethylbenzyl) phosphates

Catalytic phosphorylation of -trifluoromethylbenzyl alcohols with POCl₃ taken in a ratio of 3 : 1 under particular temperature conditions afforded predominantly symmetrical tris(-trifluoromethylbenzyl) phosphates. The latter were obtained as mixtures of two diastereomers with a statistical ratio of the components.     

Synthesis of (±)-pseudoheliotridane by allylboration of 1-pyrroline

Reaction of tricrotylborane with 1-pyrroline proceeds stereoselectively to give (1R ^* ,1′S ^* )-2-(1-methylallyl)pyrrolidine. The latter was converted to the pyrrolizidine alkaloid (±)-pseudoheliotridane through hydroboration-oxidation-intramolecular cyclization. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1450–1452, July, 1998.     

Stereogenicity/Astereogenicity as Global/Local Permutation-Group Symmetry and Relevant Concepts for Restructuring Stereochemistry

Molecules of ligancy 4 that have been derived from an allene, an ethylene, a tetrahedral, and a square-planar skeleton have been investigated to show that their symmetries are dually and distinctly controlled by point groups and permutation groups. Insomuch as the point-group symmetry was exhibited to control the chirality/achirality of a molecule, sphericity in a molecule, and enantiomeric relationship between molecules [S. Fujita, J. Am. Chem. Soc. 112 (1990) 3390], the permutation-group symmetry has been now clarified to control the stereogenicity of a molecule, tropicity in a molecule, and diastereomeric relationship between molecules. To characterize permutation groups, proper and improper permutations have been defined by comparing proper and improper rotations. Thereby, such permutation groups are classified into stereogenic and astereogenic ones. After a coset representation (CR) of a permutation group has been ascribed to an orbit (equivalence class), the tropicity of the orbit has been defined in term of the global stereogenicity and the local stereogenicity of the CR. As a result, the conventional stereogenicity has now been replaced by the concept local stereogenicity of the present investigation. The terms homotropic, enantiotropic, and hemitropic are coined and used to characterize prostereogenicity. Thus, a molecule is defined as being prostereogenic if it has at least one enantiotropic orbit. Since this definition has been found to be parallel with the definition of prochirality, relevant concepts have been discussed with respect to the parallelism between stereogenicity and chirality in order to restructure the theoretical foundation of stereochemistry and stereoisomerism. The derivation of the skeletons has been characterized by desymmetrization due to the subduction of CRs. The Cahn–Ingold–Prelog (CIP) system has been discussed from the permutational point of view to show that it specifies diastereomeric relationships only. The apparent specification of enantiomeric relationships by the CIP system has been shown to stem from the fact that diastereomeric relationships and enantiomeric ones overlap occasionally in case of tetrahedral molecules.