Phosphoramidates as Steering Elements for Highly Selective Access to Complementary Imidazo[1,2-a]pyrimidine Isomers

We report that selective N-phosphorylation of aminoimidazoles results in a key steering element that controls isomeric selectivity in the condensation of β-ethoxy acrylamides and aminoimidazoles to furnish imidazo[1,2-a]pyrimidines. We identified conditions that provide highly selective (99:1) phosphorylation at the endo- or exocyclic nitrogen. Either the 2-amino or 4-amino isomer of the (benzo)imidazo[1,2-a]pyrimidine products could be isolated in 64–95% yield. Mass spectrometric analysis and computational studies give insight into the mechanism of this exceptionally selective transformation.