Synthesis and structure of dehydro-4-iminoallantoin and its covalent adducts

Abstract

Representations of two consecutive products of the Denicke reaction were shown to be incorrect. Oxidation of uric acid ( 1a) by ferricyanide in aqueous ammonia gives 5-amino-4-iminoallantoin ( 4) and 1,5-diamino-3,7-dioxo-2,4,6,8-tetraazabicyclo[3.3.0]octane ( 5a), while methylated uric acids 1b-g afford only the corresponding end products 5. The key dehydro-4-iminoallantoin ( 6) arose on exposure of the primary adduct 4 to dilute acetic acid; a direct route to 6 was provided by oxidation of 1-iminoallantoin ( 2) with iodine. Both dehydro-allantoin ( 8) and its 4-imino analogue 6 form covalent adducts (e.g. with MeOH) at the 5-position. A brief rationale which focusses upon the stepwise nature and regiochemical course of the reaction is presented.