Transannular Cyclizations of Medium‐Sized Cycloalkynes and Cycloalkynones Induced by Electro‐ and Photochemically Generated NO3 Radicals

Transannular radical cyclizations of medium‐sized cycloalkynes and cycloalkynones induced by addition of NO3 radicals to the C–C triple bond were studied. In the reaction of NO3 with medium‐sized cycloalkynes oxidation of the triple bond to a carbonyl group occurred and formation of cis‐fused bicyclic alkanones by transannular cyclization was observed. In the reaction of NO3 radicals with medium‐sized cycloalkynones α,β‐epoxy ketones were formed in a transannular reaction sequence which can be formally considered as a retro Eschenmoser‐Ohloff fragmentation reaction. The scope and limitations of these reactions are presented and reaction mechanisms are proposed.