Switching between reaction pathways by an alcohol cosolvent effect: SmI2-ethylene glycol vs SmI2-H2O mediated synthesis of uracils.

A chemoselective switch between reaction pathways by an alcohol cosolvent effect in a general SmI2-mediated synthesis of uracil derivatives is described. The method relies on the use of coordinating solvents to increase the redox potential of Sm(II) and results in a chemoselective 1,2-reduction (SmI2–H2O) or 1,2-migration via in situ generated N-acyliminium ions (SmI2–ethylene glycol, EG). This work exploits the mild conditions of the SmI2-mediated monoreduction of barbituric acids and offers an attractive protocol for the synthesis of uracil derivatives with biological activity from readily accessible building blocks.