Abstract: A process for preparing a compound of the formula: ##STR1## wherein R.sup.1 is a hydroxyl or an amino which may optionally be substituted; R.sup.2 is a hydrogen or a C.sub.1 -C.sub.4 alkyl; and R.sup.4a and R.sup.5a together represent a group of the formula: --R.sup.6 R.sup.7 Si--O--SiR.sup.6' R.sup.7', wherein R.sup.6, R.sup.7, R.sup.6' and R.sup.7' are the same or different and each is a C.sub.1 -C.sub.4 alkyl, which process comprises reacting a reducing agent and a cyanolating agent with a compound of the formula: ##STR2## wherein R.sup.9 is an alkoxythiocarbonyl having a C.sub.1 -C.sub.4 alkyl or an arylthiocarbonyl having a C.sub.6 -C.sub.10 aryl.

Abstract: The pyrimidine compounds of the present invention are represented by the following formula: ##STR1## and pharmaceutically acceptable salts thereof, wherein, R.sup.1 represents a hydroxyl or an amino which may be substituted by an acyl group; R.sup.2 represents a hydrogen atom or an alkyl having 1 to 4 carbons; R.sup.3 represents a hydrogen or a hydroxyl; and R.sup.4 and R.sup.5 each represent a hydrogen or together form a group --R.sup.6 R.sup.7 Si--O--SiR.sup.6' R.sup.7' --, wherein R.sup.6, R.sup.7, R.sup.6' and R.sup.7' are the same or different from one another and each represent an alkyl having 1 to 4 carbons. The compounds of the present invention exhibit an excellent antitumor effect.