A practical approach for spiro‐ and 5‐monoalkylated barbituric acids

Abstract

Abstract magnified image The single step reactions of N,N′‐ substituted/‐unsubstituted barbituric acids with various alkyl dihalides under phase transfer catalytic conditions using DMF‐K 2 CO 3 (base), TBAHSO 4 (catalyst) provide spirobarbituric acids in moderate to high yields. Irrespective of the existence of C 5 ‐monoalkylated compounds in the enolic form (confirmed by the isolation of some of its analogues), the second alkylation predominantly takes place at C 5 . The underlying mechanism for the reaction is discussed. The 5,7‐dimethyl‐5,7‐diaza‐spiro[2.5]octane‐4,6,8‐trione undergoes ring opening with NaCN, PhSH, HS(CH 2 ) 2 OH and Br 2 to provide 5‐monoalkylated barbiturates which are otherwise difficult to prepare by the usual alkylation of barbituric acids.