Stereoselective Capture of N‑Acyl­iminium Ions Generated from α‑Hydroxy‑N‑acyl­carbamides: Direct Synthesis of Uracils from Barbituric Acids Enabled by SmI₂ Reduction

Lewis acid promoted cleavage of α-amino alcohols derived from barbituric acids via chemoselective Sm­(II)-mediated electron transfer affords a wide range of C6-substituted 5,6-dihydrouracils. The reaction involves the first generation of N-acyliminium ions directly from the versatile barbituric acids and proceeds with excellent stereoselectivity. The products are shown to be active in generic transition metal catalyzed reactions, thus providing a modular and highly practical sequence to the biologically significant uracil derivatives.