Organosulphur compounds-lxix1 optically active sulphinates: a new type of enantioselective asymmetric synthesis and kinetic resolution2

Optically active sulphinates with the sulphur atom as a sole centre at chirality are prepared by two methods. The first involves the reaction of symmetrical sulphites with tert-butylmagnesium chloride in the presence of optically active aminoalcohols. This new asymmetric, enantioselective synthesis affords t-butylsulphinates with 40–70% enantiomeric excess values. The second approach is based on a new type of kinetic resolution taking place when racemic sulphinates are reacted with tert-butylmagnesium chloride complexed by optically active alkaloid bases. Both the recovered sulphinates and sulphoxides formed in this reaction show moderate optical purities.     

Electrochemical synthesis of alkyl nitroaromatic compounds

Alkyl nitroaromatic compounds were readily prepared via nucleophilic aromatic substitution for hydrogen or a heteroatom by electrochemical oxidation of the sigma-complex. Butyllithium and butylmagnesium chloride were used as nucleophiles, and several nitrocompounds were tested to explore the possibilities of the NASH and NASX reactions promoted electrochemically.     

Solvent-free asymmetric aminoalkylation of electron-rich aromatic compounds: stereoselective synthesis of aminoalkylnaphthols by crystallization-induced asymmetric transformation.

Electron-rich aromatic compounds such as 2-naphthol give a faster and asymmetric 1-aminoalkylation with high yields when treated with (R)-1-phenylethylamine and aromatic aldehydes in solvent-free conditions. An asymmetric transformation of a second kind, probably induced by the preferential crystallization of one diastereomer, affords the straightforward and stereoselective synthesis of aminoalkylnaphthols. Mechanisms predictable for this asymmetric reaction are reported. The absolute configurations and the conformations of the unknown aminonaphthols are widely ascertained.     

Alkylation of non-electron rich nitrogen heterocycles by alkyl orthoformates: Quantum chemistry calculations

Results of semiempirical MO calculations of N₁- and N₂-alkyl pyrazolotriazolopyrimidin-4-ones originating from alkylation by trimethyl and triethyl orthoformate are presented.     

Alkylation of p-substituted phenols by heteropoly acids

Liquid-phase alkylation of p-tert-butylphenol (TBP) and p-cresol by olefins and benzyl chloride in the presence of solid heteropoly acids (HPA) H₃PW₁₂O₄₀ and 25% H₃PW₁₂O₄₀/SiO₂ at 100–150°C provides high yields of mono- and disubstituted products. HPAs are more active than H₂SO₄, easily separated from the reaction mixture and can be used repeatedly. -- () - () H₃PW₁₂O₄₀ 25% H₃PW₁₂O₄₀/SiO₂ 100–150°C - - . , H₂SO₄, - - .     

Solvent-controlled asymmetric Strecker reaction: stereoselective synthesis of alpha-trifluoromethylated alpha-amino acids

[reaction: see text] Stereoselective approaches to alpha-trifluoromethylated alpha-amino acids (alpha-Tfm AAs) have been developed. The stereoconfigurations of the resulting alpha-Tfm AA precursors were well controlled by using different solvents. The optically active (S)-2-amino-2-phenyl-1,1,1-trifluoropropanoic acid was synthesized by this method.     

Single-stage synthesis of alkyl-H-phosphinic acids from elemental phosphorus and alkyl bromides

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Cobalt N-heterocyclic carbene alkyl and acyl compounds: synthesis, molecular structure and reactivity

The N-heterocyclic-carbene containing cobalt carbonyl compound [Co(IMes)(CO)3(Me)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene), 1, has been synthesised by tertiary phosphine displacement from [Co(PPh3)(CO)3(Me)]. Subsequent carbonylation afforded the acyl derivative [Co(IMes)(CO)3(COMe)], 2. Similarly, the compound [Co(IMes)(CO)3(COEt)], 3, has been synthesised. The compounds 2 and 3 have been shown to react with dihydrogen to form the cobalt hydride compound [Co(IMes)(CO)3(H)], 4. The molecular structures of compounds 1 and 2 have been determined.     

Alkylation of magnesium enamide with alkyl chlorides and fluorides

A magnesium enamide derived from N-2-(N',N'-diethylamino)ethyl imine reacts with a primary and secondary alkyl chloride or a primary alkyl fluoride to give an alpha-alkylated ketone in good to excellent yield after hydrolysis. The reaction takes place with a high level of inversion of stereochemistry at the electrophilic carbon center and will be useful for production of optically active compounds.     

The asymmetric synthesis of cyclopentane derivatives by palladium-catalyzed coupling of prochiral alkylboron compounds

Treatment of the prochiral triflate 2a with Pd₂(dba)₃·CHCl₃, (S)-(R)-BPPFOAc and K₂CO₃, in THF at 40°C, gave the cyclopentane derivative 10 in 58% yield and in 28% ee after oxidative work-up and benzoylation. Moreover, reaction of the prochiral triflate 2c with Pd₂(dba)₃·CHCl₃, (S)-(R)-PPFA and K₂CO₃, in THF at 40°C, afforded the cyclopentane derivative 3b, with a quaternary carbon center, in 42% yield and in 31% ee after oxidative work-up.