Triplet Diradicals of Pyridine N-Oxides Enable Access to Oxygenated Bicycles from Bicyclo[1.1.0]butanes

Bicyclo[1.1.0]butanes (BCBs) are versatile strain-release building blocks, yet their oxygenative transformations remain underdeveloped due to the instability of oxene intermediates. To address this challenge, we recently reported the use of pyridine N-oxide-derived triplet diradicals as stabilized oxene surrogates for BCB oxygenation. This Synpacts article highlights that work, tracing the conceptual foundations in pyridine N-oxide photochemistry and the reaction-design logic of the programmed ring-opening/reclosing sequence that underpins the transformation. The strategy provides efficient access to 5-oxa-2-oxo-bicyclo[2.1.1]hexanes (5-oxa-2-oxo-BCHex) and related oxygenated scaffolds. Notably, the 5-oxa-2-oxo-BCHex motif reproduces the exit vectors of meta-substituted benzenes, highlighting its potential as a three-dimensional bioisostere in medicinal chemistry.