Synthesis and reactions of Biginelli-compounds. Part 14.1 A rhodium-induced cyclization–cycloaddition sequence for the construction of conformationally rigid calcium channel modulators of the dihydropyrimidine type
作者:Birgit Jauk、Ferdinand Belaj、C. Oliver Kappe
DOI:10.1039/a808594c
日期:——
Conformationally rigid polyheterocycles 14a,b which mimic the putative receptor-bound conformation of dihydropyridine type calcium channel modulators are prepared in a six-step reaction sequence starting from urea, ethyl acetoacetate and 2-alkenylbenzaldehydes. The key step in the synthesis involves the regio- and diastereoselective intramolecular 1,3-dipolar cycloaddition reaction of a dihydropyrimidine-fused isomünchnone dipole. Deprotection of the CBZ-protected intermediates 13a,b leads to the desired target molecules 14a,b. Prolonged exposure of these cyclic enamines in solution to the atmosphere results in oxidation to the corresponding α-hydroxy imines 16a,b. Catalytic hydrogenation of the related N-benzyl-protected polycycle 19 furnishes the fully saturated hexahydropyrimidine derivative 20. The relative stereochemistry in 20 was established by an X-ray crystallographic analysis.
以尿素、乙酰乙酸乙酯和 2-烯基苯甲醛为起始原料,通过六步反应顺序制备出模仿二氢吡啶类钙通道调节剂受体结合构象的构象刚性多杂环 14a,b。合成的关键步骤是对二氢嘧啶融合的异¼nchnone 二极进行区域和非对映选择性分子内 1,3-二极环加成反应。对 CBZ 保护的中间体 13a,b 进行脱保护处理后,可得到所需的目标分子 14a,b。这些环烯胺在溶液中长时间暴露于大气中会氧化成相应的δ-羟基亚胺16a,b。对相关的 N-苄基保护多环 19 进行催化氢化,可得到完全饱和的六氢嘧啶衍生物 20。通过 X 射线晶体分析确定了 20 的相对立体化学结构。