Studies on the Synthesis of Specifically Fluorinated 4-Amino- pyridine Derivatives by Regioselective Nucleophilic Aromatic Substitution and Catalytic Hydrodefluorination
作者:Gabriel Podolan、Phillip Jungk、Dieter Lentz、Reinhold Zimmer、Hans-Ulrich Reissig
DOI:10.1002/adsc.201500393
日期:2015.10.12
titanocene difluoride as pre-catalyst and diphenylsilane as reducing agent we were able to selectively remove fluorine substituents at positions C-2 and C-4 of a variety of 4-aminopyridine derivatives. This protocol allows the synthesis of compounds such as the divalent chiral 4-(dimethylamino)pyridine (DMAP) analogue (R,R)-trans-N,N′-dimethyl-N,N′-bis(pyridin-4-yl)cyclohexane-1,2-diamine with fair overall
研究了五氟吡啶和2,4,6-三氟吡啶与一系列伯胺和仲胺的反应。在所有情况下,五氟吡啶的亲核芳香取代都具有较高的区域选择性,可提供预期的4-氨基吡啶衍生物,且产率极高,而2,4,6-三氟吡啶的区域选择性则取决于进攻性亲核试剂的空间位阻。小亲核试剂(例如吗啉)会高度优先地攻击吡啶环的4位,而体积更大的二胺会攻击2位和4位,从而导致形成三种区域异构产物。(R,R)-1,2-二氨基环己烷为中等体积的二胺,与2,4,6-三氟吡啶反应,以30%的收率得到所需的双(4-氨基吡啶基)环己烷衍生物。对于加氢脱氟,检验了两种方法。使用肼和随后的硫酸铜(II)的两步过程仅除去了一个氟取代基,但收率不足以还原更复杂的底物。用二茂钛二氟化物作为前催化剂和二苯基硅烷作为还原剂,我们能够选择性地除去各种4-氨基吡啶衍生物的C-2和C-4位上的氟取代基。该方案允许合成化合物,例如二价手性4-(二甲基氨基)吡啶(DMAP)