Free-radical functionalisation of vinylcyclopropanes

Free-radical mediated cyclopropane ring opening of 2-silylbicyclo[3.1.0]hexane 1 has been carried out leading to the corresponding trisubstituted cyclopentenes 5 and 6 in good yield with complete 1,2-stereocontrol. [3+2]-Annulation has also been performed by trapping the resulting radical with electron-rich and electron-poor olefins, leading to the corresponding polycyclic compounds. Further studies on the functionalisation of dihydropyridines and pyrroles using this methodology is also described.     

α-Diimines as nitrogen ligands for ruthenium-catalyzed allylation reactions and related (pentamethylcyclopentadienyl) ruthenium complexes

The new Cp*Ru(II) (Cp*: pentamethylcyclopentadienyl) complexes Cp*(dab-R)RuCl, [Cp*(dab-R)(MeCN)Ru][PF₆] (dab-R: RNCH-CHNR; R: iso-propyl, mesityl), and [Cp*(cod)(MeCN)Ru][PF₆], are synthesized in high yields by reacting the corresponding α-diimine or 1,5-cyclooctadiene with [Cp*RuCl]₄ and [Cp*(MeCN)₃Ru][PF₆], respectively. The α-diimine ligands are strongly bonded to the ruthenium centre as shown by the subsequent formation of the alkynyl derivatives Cp*(dab-R)RuCCR′ (R′ = tert-butyl or phenyl) and of the cationic derivatives [Cp*(dab-R)(L)Ru][PF₆] (L = CO, PMe₃). The neutral and cationic α-diimine or 1,5-cyclooctadiene ruthenium complexes are compared as catalyst precursors for the ruthenium-catalyzed allylation of diethyl-sodiomalonate and diethylamine with cinnamyl acetate or ethyl cinnamyl carbonate.     

Determination of maleic hydrazide residues in cured tobacco by gas chromatography.

A rapid and sensitive method for measuring maleic hydrazide (6-hydroxy-2H-pyridazin-3-one) residues in cured tobacco is described. A mixture of free and bound maleic hydrazide is extracted with hydrochloric acid in which maleic hydrazide glycoside is simultaneously hydrolysed. The free maleic hydrazide obtained is methylated using dimethyl sulphate and the derivative is partitioned into chloroform and determined by capillary gas chromatography using a nitrogen-phosphorus detector. The limit of detection of maleic hydrazide is 5 ppm.     

Total synthesis of hyacinthacine A1 and 3-epi-hyacinthacine A1

[reaction: see text] Total synthesis of hyacinthacine A(1) and its epimer at C3 is described. The synthesis includes a stereocontrolled carboazidation of a chiral allylsilane as a key step. C-Si bond oxidation and reduction of the azide, with ring-closure, complete the total synthesis, which establishes the absolute configuration of 3.     

Proprietes Zeolithiques des ferrocyanures mixtes: Isothermes d'adsorption et caracterisation de K2Zn3[Fe(CN)6]2, 9 H2O

K₂Zn₃[Fe(CN)₆]₂, 9 H₂O crystallises in the rhombic system. Lattice parameters are a = 12.941 Å, α = 58.01°. Thermal behaviour of this compound, studied by differential thermal analysis, thermogravimetric analysis and X-ray diffractometry, permitted the determination of the conditions for activation. The adsorption isotherms confirm the zeolitic character of this iron cyanide with a relative important adsorption capacity. The water is released in two steps with a contraction of the lattice.     

Preparation by yeast reduction and determination of the sense of chirality of enantiomerically pure ethyl (−)-4,4,4-trichloro-3-hydroxy- and (+)-4,4,4-trifluoro-3-hydroxybutanoate

Reduction of ethyl 4,4,4-trichloro- and 4,4,4-trifluoro-3-oxobutanoate by fermenting baker's yeast (Saccharomyces cerevisiae) on a preparative scale (20–50 g in ca. 3 1 of H₂O) gave 70–80% yields of the trichloro- [(?)-(S)- 1a ] and trifluoro-hydroxyesters [(+)-(R) 2a ] of ca. 85 and 45% ee, respectively. Both, (?)- 1a and (+)- 2a could be obtained in > 98% ee by subsequent crystallization (of(?)- 1 , (+)- 2a or the 3,5-dinitrobenzoate (+)- 2b . The absolute configuration of both hydroxyesters was determined (a) by chemical correlation ((?)- 1a ), (b) from the melting diagrams and mixed melting points (differential-scanning calorimetry Fig. 1) of the dinitrobenzoates of the CF₃-derivative (+)- 2a and its CH₃-analogue 8 , and c) by X-ray analysis of the ester 2f from (+)- 2a and (?)-camphanoyl chloride (Fig. 2 and 3).     

N,Se-Acetals: Preparation and use in diastereoselective radical reactions

A new facile synthesis of N,S- and N,Se-acetals starting from aldehydes and primary amines is presented (Schemes 3–5). These acetals are used as precursors for stereoselective radical deuteration and allylation reactions (Schemes 6 and 7, Tables 1 and 2). The stereochemical outcome of the reactions depends on the radical trap and the substituents at the N-atom. Deuterations give always anti products with moderate to high selectivities. The allylation reactions give either syn or anti products with low to moderate selectivities. The observed stereoselectivities can be explained with a model based on minimization of A^1,3 strain and are controlled by steric and stereoelectronic effects.