Quinoline-Dependent Electronic Response and Acyl Group Control of Linker Cleavage in a Folded Nitrene Precursor.

A 2-methylquinoline-derived, O-benzoylhydroxylamine nitrene precursor underwent unproductive linker cleavage, whereas a related naphthalene analog did not. To clarify the origin of this structure-dependent behavior, we examined the conformations and excited states of the two precursors using density functional theory (DFT) and time-dependent DFT calculations. Both precursors preferentially adopted folded aryl/benzoate conformations, indicating that folding alone is not a sufficient discriminator. Instead, the quinoline precursor showed a lower and more allowed excitation than the naphthalene control, together with a mixed local/partial benzoate-directed electronic density redistribution in the selected excited states. Replacing the benzoyl group of the quinoline precursor with an acetyl group retained the high reactivity, giving the corresponding cyclized product in 83% yield after 3 h, with linker cleavage diminished significantly. These results support a qualitative model in which the folded benzoyl-containing precursor enables an off-pathway electronic response, whereas acyl-group tuning strongly suppresses the cleavage channel.