A highly diastereoselective synthesis of homoallylic alcohol/amine appended uracils: the role of the uracil C-4 carbonyl in diastereoselectivity control

5-Formyluracil derivatives and their Schiff bases with chiral amino alcohols undergo highly diastereoselective 1,2- and 1,3-allylations. The absence of the C-4 carbonyl in the case of 2,4-dimethoxy-5-formylpyrimidine and its Schiff bases leads to loss of diastereoselectivity.