Stereoselective synthesis of dihydropyrimidinethione podand in the presence of l-proline or 4-hydroxy-l-proline and metal nitrates

The asymmetric Biginelli reaction involving a 3-oxobutanoyl-containing podand, benzaldehyde, and thiourea was studied using secondary amines as a chiral inductor, Brönsted acid as a catalyst, and metal salts (especially metal nitrates) as an additive of asymmetric catalysis (AAC) was studied. The tuberculostatically active dihydropyrimidine-thione-containing podand was synthesized with an enantiomeric excess of 57% in the presence of 4-hydroxy-l-proline. In the presence of metal nitrates, the influence of the ionic radius of the cation on the enantioselective excess of the reaction under study was observed, which made it possible to propose a possible mechanism of chiral induction controlled by the complexing ability of the initial β-ketoester-containing podand with metal ions and coordination of the reagents in the transition states.