NO3• Induced Self-Terminating Radical Oxygenations: Diastereoselective Synthesis of Anellated Pyrrolidines

Abstract

Anellated pyrrolidines 19–22 were obtained through a diastereoselective self-terminating, oxidative radical cyclization cascade by treating the cis-cyclopentyl substituted alkynyl amines 14–18 with photochemically generated nitrate radicals, NO3●. A fast and modular access to the starting materials 14–18 was developed, which readily enables variation of the substitution pattern at the pyrrolidine ring formed upon radical cyclization. The diastereoselectivity of this reaction sequence was found to be strongly influenced by the nature of the substituents at the nitrogen atom. This shows that a complex interplay of both steric and stereoelectronic effects orchestrates the stereoselectivity of 5-exo radical cyclizations of highly substituted radicals.