Regioselective Aryl Radical Cyclization: Access to Pyrimidine-Annelated Spiro Heterocycles Through 5-exo Ring Closure

Abstract

Aryl radical cyclization of a range of 6-(2¢-bromophenoxymethyl)-1,3-dimethyluracils 4a-g was carried out with tributyltin chloride and sodium cyanoborohydride in the presence of AIBN for four hours to give exclusively the '5-exo' cyclization products, 1,3-dimethylspiro[pyrimidine-6,3¢-2¢,3¢-tetrahydrobenzofuran]-2,4-diones 5a-g in 92-95% yield. The starting materials were in turn prepared in 90-92% yield by refluxing 6-chloro methyl-1,3-dimethyl uracil with various 2-bromophenols or 2-bromonaphthol in acetone in the presence of anhydrous potassium carbonate for eight hours.

Five‐Membered Heterocycles: Benzofuran and Related Systems

“…A similar approach has also been demonstrated by the same group to obtain spiro [pyrimidine-6,3 0 -2 0 ,3 0 -tetrahydrobenzofuran]-2,4-diones [48]. On the other hand, n-Bu 3 GeH is reported to be an effective alternative compared with n-Bu 3 SnH in the synthesis of 3-substituted-2,3-dihydrobenzo [b]furans [49].…”