Giuseppe Bartoli

Cerium(III) Chloride Catalyzed Michael Reaction of 1,3-Dicarbonyl Compounds and Enones in the Presence of Sodium Iodide Under Solvent-Free Conditions

Cerium(III) chloride heptahydrate in the presence of sodium iodide catalyses the Michael addition of 1,3-dicarbonyl compounds to α,β-unsaturated ketones and α,β-unsaturated aldehydes with extraordinary efficiency. The very mild conditions allow high chemoselectivity as shown by the absence of the typical side reactions, which can be observed in the conventional base-catalyzed processes. More interestingly, when at least one of the starting materials is liquid at room temperature, the reaction can also be performed without solvents. The CeCl3· 7 H2O/NaI catalyst system can be easily separated from the reaction mixture and it can be reused without an appreciable loss of activity. Advantages of the present procedure, which utilizes cheap and “friendly” reagents, over the previously reported ones, are discussed.

Grignard reagents selective attack to nitroarenic function in the presence of other electrophilic groups

Abstract Exclusive alkylation of the nitroarenic system takes place in competitive reactions of RMgX with nitrobenzene and various electrophiles such as ketones, esters, cyano-and iodo-derivatives and in reactions with some functionalized nitrobenzenes, only aldehydes show comparable reactivity.

Mechanism and Extensibility of the Reaction

Alkylcerium reagents add to the multiple bonds of allyl and propargyl alcohols in good yields and under mild conditions. The double bond can be reduced with lithium aluminum hydride in the presence of cerium trichloride. The regiochemistry of the attack depends on electronic factors.

Mechanistic studies on the reaction of nitro- and nitrosoarenes with vinyl Grignard reagents

The reaction of ortho-substituted nitrobenzenes with 3 mol vinylmagnesium halides gives mainly 7-substituted indoles together with minor amounts of the aniline from complete reduction of the nitroarene. Under the same experimental conditions, para-substituted nitrobenzenes essentially lead to the corresponding anilines, with indoles being recovered in very low yield. Nitrosoarenes react with 2 mol Grignard reagent to give almost the same product distribution. An accurate analysis of the stoichiometry of the reaction established that in the first stage of the reaction nitroarenes are attacked at the oxygen atoms and are reduced to nitrosoarenes via enolate elimination. The nitroso derivative can undergo a 1,2-addition to give an N-aryl-N-vinylhydroxylamino magnesium salt. Hydrolysis of this intermediate affords hydroxylamine and the carbonyl derivative corresponding to the vinyl Grignard reagent, as proved by the reaction of nitroarenes with 2 mol Grignard reagent. In the presence of an excess of vinyl magnesium halide, a complete reduction to vinylaniline derivatives, which hydrolyse to aniline, occurs. The effect of the bulkiness of the substituent both in the nitroarene and in the Grignard reagent, the orientation of alkylation and the relative reaction rates of indole and aniline formation suggest that indoles arise via a completely different route: i.e. an inverse 1,2-addition to the NO double bond. The N-aryl-O-vinylhydroxylamino magnesium salt intermediate can undergo a [3,3]-sigmatropic rearrangement followed by a rapid ring closure. The third mole of Grignard reagent acts as a base on this bicyclic intermediate, re-aromatizing the six-membered ring. Elimination of water ultimately leads to the indole.

Addition of organocerium reagents to homoallyl alcohols

Abstract Alkylcerium reagents and hydride ions add to multiple bonds of homoallyl alcohols under mild conditions, leading to saturated alcohols in good yields.

Fluorodenitration of some mildly activated nitro-compounds

1-Fluoro-3-nitrobenzene, 2- and 4-fluoropyridines, and 2-fluorothiazole have been synthesised from the corre-sponding nitro-derivatives by treatment with fluoride ion in hexamethylphosphoramide or N-methyl-2-pyrrolidone.

N-allylhydroxylamines from 1,2-addition of allyl Grignard reagents to nitro compounds: generality and drawbacks of the reaction

Allyl Grignard reagents react with both aromatic and aliphatic nitro derivatives via 1,2-addition to the nitro group. Conversely, nitroalkenes give either intractable mixtures or exclusive 1,4-conjugate addition. Nitroarenes with high steric hindrance at the ortho position and low aromatic stabilisation give competitive or exclusive conjugate addition at the reactive para position. The ‘in situ’ treatment of the unstable 1,2-adducts with aluminium hydrides in the presence of catalytic amounts of palladium on charcoal provides a general method of synthesis of N-allylhydroxylamines. LiAlH4 is a very efficient reducing agent, but, in some cases, it does not allow the reduction to be stopped at the hydroxylamino stage. Red-Al® and DIBAL-H are less efficient but they ensure greater selectivity. Red-Al avoids the complete reduction to amines except when a strongly electron-donating substituent such as a methoxy group is present in the para position of the aromatic ring. Hydroxylamines can be obtained by reaction of nitrosoarenes followed by aqueous quenching. However, this alternative reaction does not offer any improvement, since relevant amounts of azo and azoxy derivatives are recovered as by-products.