Thiourea is often the reagent of choice for synthesising pyrimidines. If a sulphur free pyrimidine is required the sulphur needs to be removed oxidatively or reductively.
Reduction is typically carried out using Raney Nickel. A new reduction method has recently been published by chemists at Merck. In this new method Heterocyclic thioethers are leaved with triethylsilane and palladium on carbon in THF.
There are over 30 examples listed in the paper including pyrimidines, pyrazines pyridazines, oxazoles, benzoxazoles and purines and yields for the vast majority of substrates are 80-96%. Two yields are 60-67% and in one case (an ethylthiopyridazine) the yield is only 30%. The method tolerates ketone, ester, amine, and cyclopropylamino groups as well as alkyl groups, benzyl groups and methoxy substituents.
T.H. Graham, W. Liu, and D.M. Shen, Org. Lett., 2011, 13, 6232-6235.