Cyclization of Imides to 2-Azabicycles via Aminoketyl Radicals by Using Samarium(II) Iodide–Water: Reaction Development, Synthetic Scope, and Mechanistic Studies

^◊ To whom correspondence about crystallographic data should be addressed

Dedicated to Professor Henri Kagan

Abstract

The first highly selective method for direct addition of aminoketyl radicals [R–C^•(O^–)NR¹R²], generated from five- or six-membered cyclic imides, to nonactivated π-systems by using the SmI₂–H₂O reagent is reported. The transformation is operationally simple, scalable, and provides access to valuable angular 2-azabicycles containing three contiguous stereocenters with excellent diastereoselectivity (>95:5 dr). The protocol accommodates a wide range of π-acceptors that can be modulated by the alcohol additive used. Notably, the transformation provides the first general method for generation of aminoketyl radicals by a direct electron capture to amide bonds, thus opening new vistas for applications of these underutilized intermediates in a diverse array of open-shell reaction pathways. Systematic studies on the effects of additives, the scope and limitations of the reaction, and the reaction mechanism are reported.

Key words

azabicycles - samarium diiodide - reductive coupling - aminoketyl radicals - stereoselectivity - cyclizations - umpolung

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