作者:Simonetta Orlandi、Gianluca Pozzi、Mauro Ghisetti、Maurizio Benaglia
DOI:10.1039/c3nj00807j
日期:——
Three enantiopure fluorous thioureas featuring a free –NH2 group were synthesized by direct addition of aromatic isothiocyanates bearing a single n-C8F17 substituent in the ortho, meta and para position, respectively, to enantiopure (1R,2R)-1,2-diaminocyclohexane. The catalytic behavior of these bifunctional molecules was assessed in representative Michael-type reactions. The three fluorous thioureas performed similarly in all the reactions tested, thus showing that the position of the fluorous ponytail does not have a major influence on the catalytic behavior of this class of compounds. In particular, excellent enantioselectivities (up to 99% ee) and yields (up to 98%) were obtained for the addition of aliphatic aldehydes to maleimides to give α-substituted succinimides. Recyclability of these primary amine-based thioureas was found to be limited by the concurrent formation of imine-derivatives during the catalytic process, leading to a structural modification of the organic catalyst.
通过将分别在正位、偏位和对位具有单个 n-C8F17 取代基的芳香族异硫氰酸酯直接加到对映体 (1R,2R)-1,2-二氨基环己烷上,合成了三种具有游离 -NH2 基团的对映体荧光硫脲。在具有代表性的迈克尔型反应中,对这些双功能分子的催化行为进行了评估。这三种有荧光的硫脲类化合物在所有测试反应中的表现相似,从而表明荧光马尾的位置对这类化合物的催化行为没有重大影响。特别是在脂肪醛与马来酰亚胺的加成反应中,获得了极好的对映选择性(ee高达 99%)和收率(高达 98%),从而得到了 α-取代的琥珀酰亚胺。研究发现,这些伯胺基硫脲的可回收性受到催化过程中同时形成的亚胺衍生物的限制,从而导致有机催化剂结构的改变。