Convenient Access to Ferrocene Fused <i>aza</i>-Heterocycles via the Intramolecular Ritter Reaction: Synthesis of Novel Racemic Planar-Chiral 3,4-Dihydroferroceno[<i>c</i>]pyridines and 1<i>H</i>-Ferroceno[<i>c</i>]pyrroles

Abstract

An efficient and easy approach to the synthesis of novel racemic planar-chiral 3,4-dihydroferroceno[c]pyridines and 1H-ferroceno[c]pyrroles via the intramolecular Ritter reaction of 2-ferrocenyl-3,3-dimethylbutan-2-ol with nitriles and thiocyanates in the presence of MeSO3H was developed. Aromatic and aliphatic nitriles, phenylacetonitriles, and β-oxonitriles produced exclusively 3,4-dihydroferroceno[c]pyridines. The condensation of 2-ferrocenyl-3,3-dimethylbutan-2-ol with various thiocyanates, including alkyl thiocyanates, benzyl thiocyanate, and ethyl 2-thiocyanatoacetate, yielded not only 3,4-dihydroferroceno[c]pyridines but also 1H-ferroceno[c]pyrroles. The selectivity of these reactions depended on the temperature and the order of addition. The size of substituents at the α-position to the sulfur atom of thiocyanates also had a significant effect on the distribution of products.

Keywords

• <i>α</i>-ferrocenyl alkyl alcohol
• 3,4-dihydroferroceno[<i>c</i>]pyridine
• 1<i>H</i>-ferroceno[<i>c</i>]pyrrole
• MeSO₃H
• carbocation
• nitrile