Andrzej Kwast

Vicarious nucleophilic substitution of hydrogen. Mechanism and orientation

Hydrogens located at activated positions in electrophilic arenes, e.g. ortho and para hydrogens in nitrobenzenes, can be replaced with a nucleophile moiety provided there is at least one nucleofuge X connected to the nucleophilic centre. As the group really leaving in this hydrogen substitution process is not the hydride anion but X, the reaction has been named vicarious nucleophilic substitution of hydrogen (VNS). The concepts on the mechanism of the reaction and their experimental background are presented. Reactivity and orientation—the fundamental questions concerning synthetical applications of VNS—are discussed in light of the supposed mechanistic picture.

Vicarious nucleophilic substitution of hydrogen in electrophilic alkenes

Abstract Carbanions containing leaving groups react in the presence of base with electrophilic alkenes giving products in which vinylic hydrogen is replaced with the carbanion moiety. They are formed via addition - β-elimination pathway analogous to the vicarious nucleophilic substitution in nitroarenes. In some cases, however, the cyclization - ring opening process takes place instead.

Effect of base concentration on the rate of the vicarious nucleophilic substitution of hydrogen and on the kinetic isotope effect

Abstract Varying concentration of the chloromethyl tolyl sulfone carbanion influences the rate of its VNS reaction with 2-fluoro-4-bromonitrobenzene and changes the mechanistic scheme from thermodynamic to kinetic control. Both primary and secondary kinetic isotope effects are observed and are clearly connected with particular kinetic relations.

Stereochemical control of the interfacial darzens condensation

The condensation of α-chlorophenylacetonitrile (1) with benzaldehyde (2) carried out in the presence of 50% aq. NaOH and a quaternary ammonium catalyst gives trans-2,3-diphenylglycidonitrile, while without the catalyst, the cis-isomer predominates; in the latter case the reaction proceeds at the interface.

Reactions of nitrosalicylic aldehydes with chloromethyl tolyl sulfone anion. Synthesis of 2-hydroxydihydrobenzofurans

Abstract Vicarious nucleophilic substitution of hydrogen (VNS) with chloromethyl tolyl sulfone carbanion does not occur in 3-, 4- and 5-nitrosalicylaldehydes. Instead, nucleophilic addition to the carbonyl group takes place leading to 2-hydroxydihydrobenzofurans. The same reaction course is observed for other salicyl aldehyde derivatives.

Vicarious nucleophilic substitution of hydrogen in nitrophenyl toluenesulfonates

Abstract Toluenesulfonates of nitrophenols react with carbanions possessing leaving groups giving products of the vicarious nucleophilic substitution of hydrogen. The yields and orientation depend on the reaction conditions and the structure of the reagents. The products obtained can be easily hydrolyzed to the corresponding phenols or — in certain cases — to hydroxynitrobenzaldehydes.

Nucleophilic substitution of hydrogen in electrophilic alkenes

Carbanions containing leaving groups replace hydrogen in electrophilic alkenes via an addition–base induced β-elimination pathway.

General synthesis of 2,1-benzisoxazoles (anthranils) from nitroarenes and benzylic C–H acids in aprotic media promoted by combination of strong bases and silylating agents

Carbanions of phenylacetonitriles, benzyl sulfones, and dialkyl benzylphosphonates add nitroarenes at the ortho-position to the nitro group to form

Reactions of organic anions. 122. Reactions of carbanions with carbon tetrachloride in two-phase systems. Chlorinated products as nucleophilic and electrophilic intermediates

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