Diastereoselective synthesis of 2-substituted-piperidin-4-ones as convenient precursors for an asymmetric approach to carbacephams

Optically active carbacephams can be efficiently prepared generating the β-lactam ring on 2-substituted-piperidin-4-ones. These can, in turn, be prepared diastereoselectively through a Michael-Michael reaction sequence initiated by benzylamine on precursors derived by Wittig reaction between serinals and 4-[(4-methylphenyl)sulfonyl]-1-(triphenylphosphoranylidene)-2-butanone.     

Sequential one-pot InBr(3)-catalyzed 1,4- then 1,2-nucleophilic addition to enones

Low sensitivity toward traces of moisture and high tolerance of different functional groups make indium tribromide suitable for carrying out multistep synthetic sequences. In particular, we have realized a 1,4-conjugated addition of indoles/thiols to alpha,beta-unsaturated ketones mediated by a catalytic amount (10 mol %) of InBr(3) obtaining the desired beta-substituted ketones in good yields. The Lewis acidity of indium salts was not affected by coordinating and acid nucleophiles; therefore, the subsequent catalytic 1,2-addition of Me(3)SiCN to carbonyl compounds can be performed in one pot. With the optimized atom-efficient protocol, several polyfunctionalized alpha-silyloxy cyanohydrins were synthesized in good to excellent yields (up to 97%) and a notable level of simple 1,3-diastereoselection (up to 84:16) was recorded in the case of 2-cyclohexen-1-one 2c.     

A new nitrile oxide based synthesis of the antitumor agent geiparvarin

Geiparvarin 1 has been synthesized utilizing the 3,5-disubstituted isoxazole 8 as protected synthon for the 3(2h)furanone system, the desired α′-hydroxy-1,3-diketone precursor being eventually revealed by Mo(CO)₆ promoted reductive cleavage.     

Highly dispersed potassium on alumina as a metalating agent. Alkylation of enolizable compounds

Highly dispersed potassium on alumina (K/Al₂O₃) acts as a metalating agent towards enolizable compounds and the intermediate organopotassium derivatives can be alkylated with primary alkyl bromides. The reaction conditions are dependent on the substrate. In particular, tetrahydrofuran is the solvent of choice for the metalation of nitriles and aldehydeN,N-dimethylhydrazones at ?60°C and of N-cyclohexyl ketimines at room temperature, whereas hexane must be used for ketones.     

Highly reactive metals from potassium—graphite. Preparation and use of titanium—graphite and tin—graphite

The potassium—graphite route to active forms of metals has been extended to the preparation of titanium—graphite (Ti---Gr) and tin—graphite (Sn---Gr). The Ti---Gr is used to achieve the reductive coupling of ketones to give alkenes, and Sn---Gr is used in the preparation of diallyltin dibromide complexes which react with aldehydes to give homoallylic alcohols.     

Adsorption of succinonitrile at the mercury-aqueous solution interface: Unusual role of a fixed dipole in the adsorbed molecule

The adsorption of succinonitrile (SN) on a polarized Hg electrode has been studied from 0.25 M NaF aqueous solutions by means of both capacity and electrocapillary curves. Adsorption isotherms have been found to be strictly congruent with respect to both charge and potential. The charge of maximum adsorption is at ?4.6 μC cm^?2 and ΔG_ads⁰, the free energy of adsorption at zero coverage, decreases more rapidly as the charge is made positive with respect to O_max^M than on the other side. The adsorption obeys a Frumkin isotherm with a=?1.87 corresponding to attraction and saturation concentration of 4.8×10^?10 mol cm^?2 corresponding to an area per molecule of about 34.5 Ų. Experimental results suggest that SN adsorbs flat on the surface but, unlike acetonitrile and propionitrile, the CN groups are slightly turned towards the solution. This is responsible for the absence of electronic interaction of the CN groups with the metal at positive charges, which is apparent with the other two nitriles. Implications of the particular structure of the adsorbed molecule on the other adsorption parameters are discussed in detail.     

New catalytic approaches in the stereoselective Friedel-Crafts alkylation reaction

After more than 125 years, the Friedel–Crafts alkylation is still one of the most studied and most utilized reactions in organic synthesis. What is the secret of this astonishing success? Perhaps the great versatility in scope and applicability continues to justify its crucial role in the synthesis of more and more complex molecules. However, it has taken more than a century for asymmetric catalytic versions of this reaction to be developed and subsequently extended to a range of aromatic compounds and alkylating agents. Herein we review recent developments in the design and use of catalytic and stereoselective strategies for the alkylation of aromatic systems and synthesis of a wide range of polyfunctionalized enantiomerically enriched compounds.     

A new enantiodivergent synthesis of the Geissman-Waiss lactone

Intramolecular Michael reaction of methyl (R)-6-(tert-butoxycarbonylamino)oxy-4-hydroxy-2-hexenoate, in turn obtained from tert-butyl (R)-3-hydroxy-4-pentenoate, paved the way to the synthesis of both enantiomers of 2-oxa-6-azabicyclo[3.3.0]octan-3-one (the Geissman-Waiss lactone), a precursor for necine bases. Key intermediates in this approach were represented by enantiomeric bicyclic lactones incorporating a [1,2]-oxazinane nucleus, which has been conveniently used to install the pyrrolidine framework of the target compounds through a synthetic scheme featuring the reduction of the nitrogen-oxygen bond and an intramolecular S_N2 reaction.     

Enantioselective organocatalyzed Henry reaction with fluoromethyl ketones

Remarkable generality in scope of new C9-benzoylcupreines bearing electron-withdrawing substituents for the nitroaldol condensation with fluoromethyl ketones is presented. Both tri- and difluoromethyl ketones provided excellent levels of stereoinduction (ee 76-99%) under mild reaction conditions and low loading of catalyst (1-5 mol%).     

Periastron shift in Weyl class spacetimes

The periastron position advance for geodesic motion in axially symmetric solutions of the Einstein field equations belonging to the Weyl class of vacuum solutions is investigated. Explicit examples corresponding to either static solutions (single Chazy-Curzon, Schwarzschild and a pair of them), or stationary solutions (single rotating Chazy-Curzon and Kerr black hole) are discussed. The results are then applied to the case of S2-SgrA^* binary system of which the periastron position advance will be soon measured with a great accuracy.