Diversity-Oriented Synthesis of a Library of Star-Shaped 2H-Imidazolines

A library of star-shaped 2H-imidazolines has been synthesized via Debus-Radziszewski condensation from 1,2-diketones and ketone starting materials. Selective reduction of one imine group of the 2H-imidazole intermediate with LiAlH4 or catalytic flow hydrogenation furnished 2H-imidazolines, which could be conveniently diversified by reacting the amine N with electrophiles, resulting in a set of 21 amide-, carbamate-, urea-, and allylamine-containing products. In total, five points of diversification could be used, which allow the production of a set of functionally diverse compounds. The synthesis of acylated 2H-imidazolidines resulted in intrinsically labile compounds, which spontaneously degraded to acyclic derivatives, as shown for the reaction of 2H-imidazolidine with hexylisocyanate.