Conformational Control and Photoenolization of Pyridine-3-carboxaldehydes in the Solid State: Stabilization of Photoenols via Hydrogen Bonding and Electronic Control
intramolecular hydrogen bonding could be utilized to achieve conformational control. In contrast to mesitaldehydes, which undergo efficient photocyclization to benzocyclobutenols in the solid state, the heteroatom analogues 1b and 1c exhibit a perceptible color change (from colorless to pale yellow for 1b and yellow-orange for 1c) upon UV irradiation; the color attributed to (E)-enols is persistent for