Towards a General Access to 1‐Azaspirocyclic Systems via Photoinduced, Reductive Decarboxylative Radical Cyclizations

A convenient and versatile approach to important 1‐azaspirocyclic systems relevant to medicinal chemistry and natural products is reported herein. The main strategy relies on a reductive decarboxylative cyclization of redox‐active esters which can be rapidly assembled from abundant cyclic azaacids and tailored acceptor sidechains, with a focus on alkyne acceptors enabling the generation of useful exo‐alkene moieties. Diastereoconvergent variants were studied and could be achieved either through remote stereocontrol or conformational restriction in bicyclic carbamate substrates. Two sets of metal‐free photocatalytic conditions employing inexpensive eosin Y were disclosed and studied experimentally to highlight key mechanistic divergences. A simple yet versatile strategy for the construction of important 1‐azaspirocyclic scaffolds is described. Alkynyl‐tethered N‐hydroxyphthalimide esters, swiftly assembled through an alkylation/deprotection/activation sequence, undergo photoinduced reductive decarboxylative radical 5‐exo and 6‐exo‐dig cyclizations employing eosin Y (EY) as inexpensive photocatalyst. The key step can proceed in a diastereoconvergent manner and affords diverse ring systems relevant to medicinal chemistry and natural products.