Conformational and stereoelectronic control in ring-transformations of<i>cis</i>-4,5-dialkoxytetrahydropurine-2,6,8-triones
作者:Nevenka Poje、Antun Palković、Mirko Poje
DOI:10.1002/jhet.5570340220
日期:1997.3
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 (R1 = R3 = Me, R7 = 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
在位置4的4,5-二甲氧基四氢嘌呤-2,6,8-三酮2的发散酸催化的开环,生成1-(5-甲氧基乙内酰脲-5羰基)脲4(R 7 = Me)或5-甲氧基-5-ureido-2,4,6-嘧啶三酮5(R 7 = H)可以通过假设其优先选择与N-取代作用相关的顺式融合系统的两个构象异构体之一来合理化。分子内酰胺基转移5 → 4大概是通过双环酸氨基型中间体3发生的,迄今被误分配为反应产物。与5(R 1 = R 3 = Me,R 7 = H)的情况下遇到一个好奇的碱催化重排,提供了5-甲氧基-1,5-双(甲基氨基羰基)乙内酰脲7。构象刚性的4,5-亚乙基二氧基四氢嘌呤-2,6,8-三酮9型构型的螺旋桨的显着稳定性表明,位置4处的开环方式受强大的立体电子因子控制。但是,在加热9a(R 7 = H)的水溶液时,在1,6-键上出现了另一种开环。随后发生的脱羧重排导致1,3-二甲基丙氨酸(12)及其前体1-(2-羟基乙氧基)-2