Palladium(0)-catalysed allylation of uracils and thiouracils. Influence of the solvent on the regioselectivity of the allylation

Uracil and 5-substituted uracils are monoallylated at N-1 in H2O-CH3CN with the catalytic system Pd(OAch)(2)/P(C6H4-m-SO3Na)(3) (or tppts) although performing the reaction in H2O/THF with the system Pd-2(dba)(3)/dppb leads to diallylations at N-1 + N-3. 2-Thiouracil, 5-methyl-2-thiouracil (2-thiothymine) and 6-methyl-2-thiouracil are monoallylated at sulfur in H2O/CH3CN with the catalytic system Pd(OAc)(2)/P(C6H4-m-SO3Na)3 (or tppts). Performing the reactions in H2O/THF with the system Pd-2(dba)(3)/dppb leads to diallylations at N-1 + N-3 of 2-thiouracil and 2-thiothymine whereas 6-methyl-2-thiouracil is diallylated at S + N-3. Copyright (C) 1996 Elsevier Science Ltd