Catalytic asymmetric hydrogenation of N-Boc-protected pyrroles proceeded with high enantioselectivity by using a ruthenium catalyst modified with a trans-chelating chiral bisphosphine PhTRAP. The ruthenium catalyst prepared from Ru(eta3-methallyl)2(cod) and (S,S)-(R,R)-PhTRAP in the presence of triethylamine was the most enantioselective for the asymmetric hydrogenation of methyl pyrrole-2-carboxylate, giving the desired (S)-proline derivative with 79% ee in 92% yield. Moreover, 2,3,5-trisubstituted pyrroles bearing a large substituent at the 5-position were hydrogenated with 93-99.7% ee. The asymmetric reduction of 4,5-dimethylpyrrole-2-carboxylate gave only all-cis isomer and created three chiral centers with high degree of stereocontrol in a single process. This is the first highly enantioselective reduction of pyrroles.

中文翻译：

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2,3,5-三取代吡咯的催化不对称氢化

通过使用用转螯合手性双膦 PhTRAP 改性的钌催化剂，N-Boc 保护的吡咯的催化不对称氢化以高对映选择性进行。在三乙胺存在下由 Ru(eta3-methallyl)2(cod) 和 (S,S)-(R,R)-PhTRAP 制备的钌催化剂对吡咯-2-羧酸甲酯的不对称氢化具有最大的对映选择性，得到所需的 (S)-脯氨酸衍生物，其 ee 为 79%，产率为 92%。此外，在 5 位带有大取代基的 2,3,5-三取代吡咯以 93-99.7% ee 氢化。4,5-二甲基吡咯-2-羧酸酯的不对称还原仅产生全顺式异构体，并在单个过程中产生具有高度立体控制的三个手性中心。这是吡咯的第一次高度对映选择性还原。