Nitrothiophenes, vicarious nucleophilic substitution

The vicarious nucleophilic substitution of hydrogen in nitrothiophenes is of great synthetic potential (87ACR282,91S103). Carbanions bearing leaving groups (L) at the carbanion center can initially add to... 

Selected substituted thiophene derivatives may also react with nucleophiles. Primary and secondary amines react with 2-bromo-3-substituted-5-nitrothiophenes to produce 11 <95T5403>. Vicarious nucleophilic substitution of hydrogen (VNS) works generally for both 2-nitro- and 3-... 

Substituted nitrothiophenes serve as precursors for a variety of condensed thiophenes. The synthesis of thienopyrroles has been reviewed <85S143>. Treatment of (2-nitro-3-thienyl)methyl phenyl sulfone (497) with diethyl maleate in the presence of K2CO3 and 18-crown-6 gave the thienopyridine A -oxide (498) in 38% yield <92acs689>. The reaction apparently proceeds by Michael addition, followed by elimination of phenylsulfinate and cyclization. The starting material can be prepared by vicarious nucleophilic substitution discussed earlier. 

Nitrothiophene undergoes nucleophilic hydroxylation by applying potassium terf-butyl hydroperoxide, probably via a vicarious nucleophilic substitution (VNS) process. The only product was a rather unstable 3-hydroxy-2-nitrothiophene potassium salt, which could be converted into the more stable tetrabutylammonium salt (Scheme 105) [165]. 

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