Allenic Compounds and Isothiocyanates as Key Building Units in the Synthesis of Heterocycles

Reaction between lithiated allenic compounds and isothiocyanates, R'N=C=S, in most cases gives exclusively thioimidates with the allenic structure, C=C=CC(SLi)=NR 1 . These intermediates have been used in novel approaches to 2,3-dihydropyridines, pyrroles, quinolines, cyclobutanopyrrolines, and thiophene or dihydrothiophene derivatives. The procedures leading to the heterocycles with a nitrogen atom in the ring involve 5-alkylation followed by simple heating or by treatment with copper(I) halide. 2-Aminothiophenes and 2-imino-2,5-dihydrothiophenes are formed by intramolecular nucleophilic attack of the thiolate moiety on the allenic system and subsequent addition of methyl iodide or protonation. 1 Introduction 2 Generation of Allenic Lithium Compounds 3 Formation of 2,3-Dihydropyridines or Mixtures of 2,3-Dihydropyridines and Pyrroles 4 Directed Synthesis of Pyrroles 5 Synthesis of Quinolines 6 Synthesis of Cyclobutanopyrrolines 7 Synthesis of Thiophene and Dihydrothiophene Derivatives 8 Concluding Remarks.