Spectroscopic Characterization and Electrocyclic Ring Opening of Parent 2‐Azetine

ABSTRACT ( N ‐Boc)‐protected 2‐azetine serves as a suitable precursor for the generation of parent 2‐azetine. High‐vacuum flash pyrolysis experiments at 200°C induce the deprotection of the ( N ‐Boc)‐protected 2‐azetine resulting in the release of carbon dioxide and isobutene allowing the trapping of 2‐azetine in a solid argon matrix at 3 K and its spectroscopic characterization by infrared spectroscopy. The assignment is supported by isotopic labeling experiments and excellent agreement with anharmonic vibrational frequencies calculated at the B2PLYP‐D3/def2‐TZVPP level of theory. At elevated pyrolysis temperatures, 2‐azetine undergoes selective ring opening to yield 1‐azabutadiene, for which both s‐ trans ‐( E ) and s‐ trans ‐( Z ) conformers are observed. Computed reaction pathways and free‐energy profiles rationalize the temperature‐dependent product distribution and the observed torquoselectivity. These results provide fundamental insight into the structure, stability, and reactivity of 2‐azetine and establish matrix isolation as a powerful approach for accessing highly strained nitrogen heterocycles.