Franco Stegel

Different behaviour of secondary and primary amines towards 1-alkyl-3,4-dinitropyrroles

The reaction of 1-alkyl-3,4-dinitropyrroles with secondary amines gives nucleophilic aromatic cine substitution (formation of 1-alkyl-2-amino-4-nitropyrroles), whereas the reaction with primary amines follows a more complicated pattern, involving mainly a multistep ring-opening and ring-closure process, and also yielding the product of formal direct substitution, but not that of cine substitution.

Nucleophilic aromatic substitution in the pyrrole ring

2,5-Dinitro-1-methylpyrrole undergoes nucleo-philic aromatic substitution by piperidine and methoxide ion in mild conditions.

An inverted relationship between stability and rate of formation of Meisenheimer-type adducts from dinitrothiophen and trinitrobenzene derivatives

A σ-adduct (II) is formed by the action of the methoxide ion on 2,4-dinitrothiophen; the equilibrium and rate constants for this process have been determined at 25° in methanol and the striking differences between the dinitrothiophen and the trinitrobenzene systems are discussed.

Unusual conditions for cine-substitution in the pyrrole ring: isolation of a pyrroline as an intermediate

1-Methyl-3,4-dinitropyrrole (1) reacts with methoxide in methanol to yield a 2-pyrroline (2); the regiospecific acid-promoted decomposition of (2) yields 2-methoxy-1-methyl-4-nitropyrrole (3) formally the product of cine-substitution of (1).