Bifunctional chiral auxiliaries 5: The synthesis of 1,3-diacylimidazolidine-2-thiones and 1,3-diacylimidazolidin-2-ones from 1,2-diamines

Although 1,2-diamines fail to cyclise with urea, phosgene or 1,1′-carbonyl di-imidazole, they react with carbon disulphide to give the corresponding imidazolidine-2-thiones. These undergo clean diacylation to give 1,3-diacylimidazolidine-2-thiones which are readily converted to 1,3-diacylimidazolidin-2-ones on treatment with mercury (II) acetate. An alternative two-step route to 1,3-diacylimidazolidin-2-ones uses carbonyl sulphide to effect cyclisation of the 1,2-diamine to the imidazolidin-2-one, which is subsequently diacylated. The ability to convert homochiral 1,2-diamines to homochiral 1,3-diacylimidazolidin-2-ones has also been demonstrated.