Controlled reduction of pyrimidin(e)-2(1H)-ones and -thiones with metal hydride complexes. Regioselective preparation of dihydro- and tetrahydro-pyrimidin-2(1H)-ones and the corresponding thiones

Abstract

1,4,6-Trisubstituted pyrimidin-2(1H)-ones were easily reduced with sodium borohydride to give mixtures of 3-aryl-3,4-dihydro-, 1-aryl-3,4-dihydro-, and 3,4,5,6-tetrahydro-pyrimidin-2(1H)-ones. The ratio of the three products was dramatically dependent on the reaction conditions and on the nature of the 4- and 6-substituents in the pyrimidine ring. The reaction with lithium aluminium hydride is also discussed.