One-Pot Cascade Synthesis of Fused Nitrogen-Containing Heterocycles in Aqueous Media – Utility of N-Protective Groups in Intramolecular Diels–Alder Reaction of Furan

Abstract

A metal-free, thermal, intramolecular Diels–Alder (IMDA) reaction of furan in aqueous media without the use of microwave irradiation was investigated. Protection of the amine functionality and the cycloaddition reaction were performed as a one-pot, two-component process. Various nitrogen-protecting groups and their electronic and steric effects on the cycloaddition reaction were studied. The protection–intramolecular Diels–Alder reaction sequence proceeds under environmentally benign aqueous conditions, which are tolerated by substrates with a broad range of nitrogen-protecting groups such as benzyloxycarbonyl (Cbz), trityl, tert-butoxycarbonyl (Boc), trifluoroacetyl, tosyl, mesyl, and p-nosyl [(4-nitrophenyl)sulfonyl]. This study allowed the development of a stereoselective, tandem allylamine isomerization–Diels–Alder cycloaddition sequence leading to the rapid assembly of complex nitrogen-containing heterocycles in a simple one-pot process.