Divergent Synthesis of Hydropyrimidines and Imidazolines Via Hypervalent Iodine-Mediated Dearomatization.

An anion-switch strategy employing a hypervalent iodine/protic acid system achieves programmable pathway bifurcation following pyrimidine dearomatization. Changing the acid counterion precisely diverts the reaction trajectory: triflic acid promotes ring-contractive dearomatization to imidazolines, whereas hydrogen halides trigger ring-retentive dearomatization to halogenated hydropyrimidines. DFT calculations reveal that a conformationally congested hypervalent iodine intermediate constitutes the mechanistic bifurcation point. Halide anions kinetically trap this intermediate through low-barrier transition states, diverting the reaction from the ring-contractive to the ring-retentive pathway.