作者:Dominika Jakubiec、Łukasz Przypis、Jerzy W. Suwiński、Krzysztof Z. Walczak
DOI:10.3998/ark.5550190.p009.754
日期:——
1,3-Dipolar cycloaddition is a convenient method for construction of various heterocyclic systems. We applied this method for the synthesis 5-hetaryluracil derivatives where substituted uracils played the role of 1,3-dipoles or dipolarophiles. Treatment of the nitrile oxide derived from 5-formyluracil and substituted alkenes gave the appropriate 5-(4,5-dihydroisoxazol-3-yl)pyrimidine-2,4(1H, 3H)-diones, which by oxidation with N-bromosuccinimide were transformed into appropriate 5-(isoxazol-3-yl)uracils. When 5-cyanouracil was used as a dipolarophile in the reaction with nitrile oxides, generated from aromatic aldoximes, several 5-(1,2,4-oxadiazol-5-yl) uracils were obtained. An alternative reaction of 5-formyluracil with an excess of nitriles in the presence of cerium ammonium nitrate as an oxidant gave 1,2,4-oxadiazol-3-yl derivatives in moderate yields.