Work

Regio- and Stereoselective Deprotonation and Functionalization of Strained 1-Aza[n.1.0]bicycles

Year: 2026

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide Strained 1-aza[n.1.0]bicycles offer unique opportunities to rapidly assemble complex 3D heterocycles via strain-release reactivity. However, access to functionalized variants is limited by their innate instability and challenging assembly. Herein, we report a regio- and stereoselective lithiation strategy for azabicyclo[2.1.0]pentane (ABP) and azabicyclo[3.1.0]hexane (ABH), enabling direct functionalization of the strained framework. In contrast to predictions based on conventional acidity models, lithiation occurs exclusively at the exo -C2–H position in both heterocycles. The resulting organolithium intermediates undergo efficient trapping with a diverse array of electrophiles, providing access to C2/C3-substituted pyrrolidines and piperidines with full diastereocontrol upon subsequent ring-opening. Notably, upon trapping with boronic esters, ABH boronates undergo strain-promoted migration, while ABP analogues favor elimination. Extensive experimental and computational studies reveal that the exo -C2–H bond is the thermodynamic site of deprotonation and that the ABP 1,2-boronate rearrangement is outcompeted by deleterious C3 intermolecular nucleophilic addition. This work expands the synthetic utility of azabicyclic scaffolds and provides a blueprint for exploiting strained heterocycles for stereoselective synthesis.

Source: Journal of the American Chemical Society

DOI: 10.1021/jacs.6c03462