Electroreductive Intermolecular Coupling of Uracils with Aromatic Ketones: Synthesis of 6-Substituted and cis-5,6-Disubstituted 5,6-Dihydro-1,3-dimethyluracils and Their Transformation to 6-Substituted 1,3-Dimethyluracils, trans-5,6-Disubstituted 5,6-Dihydro-1,3-dimethyluracils, and 4,5,5-Trisubstituted 3-Methyloxazolizin-2-ones

摘要

The electroreductive coupling of 1,3-dimethyluracil, thymine, and 5-fluorouracil with aromatic ketones in the presence of TMSCl gave 6-substituted and cis-5,6-disubstituted 5,6-dihydro-1,3-dimethyluratils. The dehydrotrimethylsiloxylation of the adducts afforded 6-substituted arid 5,6-fused 1,3-dimethyluracils. The detrimethylsilylation of the adducts with TBAF or 1 M HCl-MeOH gave 4,5,5-trisubstituted 3-methyloxazolizin-2-ones or 3-methyloxazolizin-2-imines in addition to simply desilylated alcohols. The cis-5,6-disubstituted 5,6-dihydro-1,3-dimethyluracils were isomerized to the corresponding trans-isomers by heating in the presence of cat. DMAI) The: cis- and. trans-5,6-disubstituted 5,6-dihydro-1,3-dimethyluracils were assigned by the coupling constants J(5,6) of their H-1 NMR spectra.