Reactions of Heterocumulenes with Organometallic Reagents: XVII. One-Pot Synthesis of Alkoxy and (Alkylsulfanyl)-Substituted Pyrroles and 2,3-Dihydropyridines from Aliphatic Isothiocyanates and Lithiated Alkoxyallenes

摘要

A fundamentally new approach was developed to designing pyrrole and dihydropyridine rings from available allenes and isothiocyanates involving a single preparative stage. Applying the reaction of lithiated alkoxyallenes with aliphatic isothiocyanates we have synthesized previously unknown 1-alkyl(cycloalkyl) pyrroles and 2,3-dihydropyridines with rare alkoxy- and alkylsulfanyl substituents. It was proved that the five-and six-membered azaheterocycles formed as a result of competing reactions of direct intramolecular cyclization of S-alkylated adducts of lithiated alkoxyallenes with isothiocyanates (1-aza-1,3,4-trienes) into pyrroles and of [1,5]-sigmatropic rearrangement into conjugated 2-aza-1,3,5-trienes with subsequent closure into dihydropyridine ring (through 6π-electrocyclization).