Conformational and stereoelectronic control in ring-transformations of cis-4,5-dialkoxytetrahydropurine-2,6,8-triones

✍ Scribed by Nevenka Poje; Antun Palković; Mirko Poje

• Publisher: Journal of Heterocyclic Chemistry
• Year: 1997
• Tongue: English
• Weight: 535 KB
• Volume: 34
• Category: Article
• ISSN: 0022-152X
• DOI: 10.1002/jhet.5570340220

✦ Synopsis

Abstract

Divergent acid‐catalysed ring‐openings of 4,5‐dimethoxytetrahydropurine‐2,6,8‐triones 2 at position 4, yielding 1‐(5‐methoxyhydantoin‐5‐carbonyl)ureas 4 (R^7^ = Me) or 5‐methoxy‐5‐ureido‐2,4,6‐pyrimidinetriones 5 (R^7^ = H), can be rationalized by assuming a preference for one of two conformational isomers of the cis‐fused system, associated with the N‐substitution effects. Intramolecular transamidation 5 → 4 presumably occurs via a bicyclic acid aminal type intermediate 3, heretofore misassigned as the reaction product. A curious base‐catalysed rearrangement was encountered with the 5 (R^1^ = R^3^ = Me, R^7^ = H) cases, which afforded 5‐methoxy‐1,5‐bis(methylaminocarbonyl)hydantoins 7. Remarkable stability of the conformationally rigid propellane type 4,5‐ethylenedioxytetrahydropurine‐2,6,8‐triones 9 toward acids, shows that the mode of ring‐opening at position 4 is controlled by powerful Stereoelectronic factors. However, an alternative ring‐opening at the 1,6‐bond has occurred on heating aqueous solutions of 9a (R^7^ = H); the ensuing decarboxylative rearrangement leads to 1,3‐dimethylallantoin (12) and its precursor, 1‐(2‐hydroxyethoxy)‐2,4‐dimethyl‐3,7‐dioxo‐2,4,6,8‐tetraazabicyclo[3.3.0]octane(11).