An ionic chain mechanism for the substitution of an acetate group by the 2-Nitropropan-2-ide ion in benzylidene diacetates

Abstract

The reaction of 16 arylmethylene diacetates [benzylidene diacetates; ArCH(OAc)₂] with lithium 2-nitropropan-2-ide in dimethyl sulphoxide has been studied. With the exception of aryl rings bearing strongly electron-donating substituents a ready reaction takes place giving l-aryl-2-methyl-2-nitropropyl acetates in good yield. The mechanism of this reaction, in which an acetate group is formally substituted by a (CH₃)₂C(N0₂) group, has been shown to be an ionic chain mechanisminvolving nucleophilic cleavage of the diacetate to catalytic quantities of the corresponding arene carbaldehyde (ArCHO) which subsequently undergoes a Henry condensation followed by a transacetylation reaction. In some cases (nitro heteroaromatic derivatives) a subsequent elimination reaction gives enol-acetates [ArC(OAc)=C(CH₃)₂].