The present invention relates to nucleoside derivatives for the treatment of Hepatitis C viral infections including compounds of formula I, pharmaceutical compositions comprising these compounds and methods for treatment or prophylaxis of Hepatitis C Virus mediated diseases employing said compounds in monotherapy or in combination therapy. The present invention further provides a process for preparing 1′,3′,4′-triacyl pyrimidine nucleoside from a N, 1′,3′,4′-tetraacylpyrimidine nucleoside