Alwyn Spencer

The palladium-catalysed arylation of activated alkenes with aroyl chlorides

Abstract Aroyl chlorides react with activated alkenes in presence of a tertiary amine and a catalytic amount of palladium acetate to give arylated alkenes, specifically cinnamic acid derivatives and stilbenes. The reaction involves a highly efficient decarbonylation of the aroyl chloride. High yields can be obtained at low catalyst concentration by choice of an appropriate base. The reaction is not particularly sensitive to substituents in the aroyl chloride, although strongly electron-donating groups are advantageous (yields up to 98%). With mono-substituted alkenes E -isomers are formed with almost complete specificity. A mechanism for the reaction is proposed.

A highly efficient version of the palladium-catalysed arylation of alkenes with aryl bromides

Abstract The palladium-catalysed arylation of alkenes with aryl bromides or iodides is shown to proceed in high yields at very low palladium concentration when carried out in a suitable strongly polar solvent with a carboxylate anion as base. The preferred combination is N , N -dimethylformamide with sodium acetate. The reaction is markedly dependent on the substituents in the aryl bromide, being favoured by electron-withdrawing groups. Turnover numbers up to 134,000 have been achieved.

Homogeneous palladium-catalysed arylation of activated alkenes with aryl chlorides

Abstract A study has been made of arylation of activated alkenes with aryl chlorides homogeneously catalysed by palladium acetate in the presence of triphenylphosphine or tri- p -tolylphosphine. Electron-withdrawing substituents in the aryl chloride favour the reaction. Only moderate yields could be obtained, and the maximum turnover number was 51, mainly because of precipitation of palladium metal. The probable mechanism of the reaction is discussed.

Synthesis of styrene and stilbene derivatives by the palladium-catalysed arylation of ethylene with aroyl chlorides

Abstract The arylation of ethylene with aroyl chlorides, catalysed by palladium(II) acetate, leads to styrene and stilbene derivatives. By appropriate choice of reaction conditions, particularly the ethylene pressure, the reaction can be made to produce either styrene or stilbene derivatives selectively. The reaction tolerates those common substituents which do not react with aroyl chlorides. Only trans-stilbene derivatives are formed.

Selective preparation of non-symmetrically substituted divinylbenzenes by palladium-catalysed arylations of alkenes with bromobenzoic acid derivatives

Abstract Palladium-catalysed arylation of alkenes with the three bromobenzoic acids or their acyl chlorides provides an efficient and selective method for the preparation of non-symmetrically substituted divinylbenzene derivatives. In the presence of palladium acetate and a phosphorus ligand the free acids react as aryl bromides, with the exception of 2-bromobenzoic acid. If palladium acetate is used alone as catalyst, all three bromobenzoyl chlorides react only as aroyl chlorides. Using two different alkenes a given non-symmetrically substituted divinylbenzene can be prepared by four different routes, allowing for an optimum choice of synthesis path. Substituent effects in the aromatic derivatives and the reactivity of the alkenes in arylation are the principal features to be taken into account. The reaction pathway can generally be chosen to give excellent yields in short reaction times at low palladium concentrations.

Stereochemical course of the palladium-catalysed arylation of disubstituted activated alkenes with benzoyl chloride

Abstract The palladium-catalysed arylation of ten 1,1- and 1,2-disubstituted activated alkenes with benzoyl chloride was studied. In most cases, more than one product was formed. The stereochemical course of the arylation appears to be controlled by the polarity of the double bond, the tendency to cis (suprafacial) alkene insertion and subsequent re-elimination, steric hindrance in the alkylpalladium(II) species formed on alkene insertion, and the reversible nature of the alkene elimination.

Ruthenium-catalysed rearrangements of azobenzenes: II. The preparation of 1-phenylbenzimidazoles from azobenzene derivatives and primary alcohols catalysed by ruthenium complexes☆

Abstract Carbonyl complexes of ruthenium catalyse the formation of 1-phenyl-2-alkylbenzimidazole derivatives from azobenzenes and tertiary amines. The reaction involves rearrangement of the azobenzene moiety to an N-phenyl-1,2-phenylenediamine intermediate which then undergoes alkylation at nitrogen with an alkyl group from the tertiary amine followed by ring closure and aromatization. Various ruthenium complexes serve as catalyst precursors for the reaction and the presence of carbon monoxide is required if good yields are to be obtained. RuCl3·3H2O is the preferred catalyst precursor. The yields of products formed show a marked dependence on the substituents in the azobenzene derivative. RhCl3·3H2O also catalyses the reaction, though less efficiently than ruthenium complexes.

Ruthenium-catalysed rearrangements of azobenzenes. IV: Rearrangement of deuterated azobenzenes to 1-phenylbenzimidazole and N-phenyl-1,2-phenylenediamine derivatives

Abstract The ruthenium-catalysed reactions of azobenzene- d 10 and 4,4′-disubstituted azobenzene- d 8 compounds with non-deuterated tri-n-butylamine, n-butanol or 2-propanol give 1-phenylbenzimidazole or N -phenyl-1,2-phenylenediamine derivatives. The distribution of 1 H in the aromatic rings of these products and in the recovered azobenzenes indicates that in all cases ortho -metallation of the azobenzene derivative has occurred. The significance of these and other observations for the mechanism of these reactions is discussed.

Ruthenium-catalysed rearrangements of azobenzenes. III: Preparation of N-phenyl-1,2-phenylenediamine and N1-phenyl-N2-(sec-alkyl)-1,2-phenylenediamine and derivatives thereof by the ruthenium-catalysed reaction of azobenzenes with secondary alcohols

Abstract RuCl 3 · 3H 2 O in presence of PPh 3 and a mild base and under an atmosphere or carbon monoxide catalyses the reaction of azobenzene and 2-propanol to give N -phenyl-1,2-phenylenediamine and N 1 -phenyl- N 2 -(2-propyl)-1,2-phenylenediamine. The selectivity towards the two products can be controlled by varying the amount of base (NaOAc or LiOAc) and 2-propanol used. Secondary alcohols which are less effective for N -alkylation than 2-propanol favour the former product. Substituents in the azobenzene derivative have a marked effect on the yield. Where the azobenzene derivative used permits isomer formation within the N -phenylphenylenediamine unit, all possible isomers usually occur.