Generation and application of carbodiimide anions: efficient construction of 2-aminopyrimidines via a cascade [4 + 2] annulation/aromatization sequence†

The cascade [4 + 2] annulation/aromatization reactions between carbodiimide anions and α,β-unsaturated imines are developed. This is the first report on regulating N-Ts cyanamides to participate in reactions absolutely via carbodiimide anions rather than previously reported cyanamide anions, affording a convenient method for synthesizing 2-aminopyrimidines. More importantly, this work expands the application of carbodiimides, broadening the coupling substrate scope to electrophilic partners and providing new strategies to construct six-membered N-heteroaromatic scaffolds. A stepwise mechanism, supported by DFT calculations, is invoked to explain the reaction selectivity.