Highly selective and high yield process for producing antitumor agent 1-phthalidyl-5-fluorouracil derivatives of formula (I) which comprises reacting a phthalidyl compound (II) with an amine (III) to yield the quaternary ammonium salts (IV), and reacting the latter with 5-fluorouracil. ##STR1## [wherein X is leaving group; ##STR2## is triethylamine, N-methylmorpholine, N-ethylmorpholine, and the like; R.sup.4 and R.sup.5 each is hydrogen, trialkylsilyloxy, alkoxy, nitro, cyano, carboxy, or alkoxycarbonyl].
An anticancer compound is disclosed which is represented by the formula ##STR1## wherein one of R.sup.1 and R.sup.2 is a phenyl-lower alkyl optionally having a substituent, phenyl-lower alkenyl or naphthyl-lower alkyl, the other of R.sup.1 and R.sup.2 is hydrogen or acyl, and R.sup.3 is hydrogen, acyl or tetrahydrofuranyl, or represented by the formula ##STR2## wherein R.sup.x is an optionally substituted pyridyl, Y is arylene and .alpha. is a known 5-fluorouracil derivative residue which can be converted to 5-fluorouracil in vivo and which is linked to the carbonyl by an ester or amide linkage.
