Photosensitized, Intramolecular Hydrogen Bond-Enabled oxa-Norrish II Reaction of β-Carbonyl Cyclobutanols

The Norrish reaction is a cornerstone of the edifice of photochemistry, defining the core reaction patterns of excited-state carbonyl compounds. Building on the Norrish type II reaction and the PCET mechanism, this work aims to achieve the oxa-Norrish type II reaction through selective 1,5-HAT from the hydroxyl group to the excited-state carbonyl group, facilitated by the intramolecular hydrogen bond in β-carbonyl alcohol substrates. Notably, the rationally installed cyclobutanol moiety in the β-carbonyl alcohols allows for the sequential 1,5-HAT/β-scission to generate the key 1,6-diradical intermediate. Depending on the α-substituent of β-carbonyl cyclobutanol compounds, the reaction mode could be facilely modulated to assemble 1,3-dicarbonyl compounds and cyclohexanones. Moreover, a one-pot protocol endowed with the oxa-Norrish type II/de Mayo reaction sequence enables the rapid construction of 1,5-dicarbonyl scaffolds.