胺中N-H鍵在內烯烴上的催化不對稱加成反應
作者:
小柯機器人發布時間:2020/11/4 17:07:49
美國加州大學伯克利分校John F. Hartwig研究團隊的一項最新研究,找到了將胺中N-H鍵不對稱加成到內烯烴上的催化體系,相關論文發表在2020年11月3日的《自然》雜誌上。
該課題組人員報導了一個陽離子含銥體系,用於催化包括環內和直鏈烯烴在內的一系列未活化內烯烴發生分子間加氫胺化反應,產生高光學選擇性的手性胺。這種催化劑包含一種新的配體和三氟甲磺酸胺反離子,並在反應設計中加入了2-氨基-6-甲基吡啶,作為氨替代物的同時在催化循環中促進多個步驟的反應速率。這些設計原理為在未活化內烯烴上加成N-H、O-H或C-H鍵指明了道路,大大簡化了從基本化學原料合成功能分子的過程。
加氫胺化反應,即胺中N-H鍵在烯烴上的加成反應,是一個基礎但有挑戰性的有機反應,該反應可在100%原子經濟性下,利用兩種來源充足的化學原料——烯烴和胺——生成烷基胺。這個反應尤為重要,因為胺(尤其是手性胺)是許多天然產物和藥物中常見的基團。雖然已有許多發展加氫胺化反應催化劑的努力,絕大多數發生分子間加氫胺化反應的烯烴還局限於共軛、具有環張力的或末端的烯烴;只有少數幾個案例中胺上的N-H鍵可以直接加成在未活化內烯烴上,包括最近報導的光催化加氫胺化,但發生在未活化內烯烴上的分子間手性加成尚未見諸報導。
事實上,在這篇報導之前,所有不使用導向基團、在任何未活化烯烴上直接發生的分子間手性加氫胺化反應,只能獲得很一般的光學選擇性。
附:英文原文
Title: Catalytic asymmetric addition of an amine N–H bond across internal alkenes
Author: Yumeng Xi, Senjie Ma, John F. Hartwig
Issue&Volume: 2020-11-03
Abstract: Hydroamination of alkenes, the addition of the N–H bond of an amine across an alkene, is a fundamental, yet challenging, organic transformation that creates an alkylamine from two abundant chemical feedstocks, alkenes and amines, with full atom economy. The reaction is particularly important because amines, especially chiral amines, are prevalent substructures in a wide range of natural products and drugs. Although extensive efforts have been dedicated to developing catalysts for hydroamination, the vast majority of the alkenes that undergo intermolecular hydroamination have been limited to conjugated, strained, or terminal alkenes;only a few examples occur by the direct addition of the N–H bond of amines across unactivated internal alkenes, including recent photocatalytic hydroamination, and enantioselective intermolecular additions to such alkenes are not known. In fact, current examples of direct, enantioselective intermolecular hydroamination of any type of unactivated alkene lacking a directing group occur with only moderate enantioselectivity. Here we report a cationic iridium system that catalyses intermolecular hydroamination of a range of unactivated, internal alkenes, including those in both acyclic and cyclic alkenes, to afford chiral amines with high enantioselectivity. The catalyst contains a new ligand and triflimide counteranion, and the reaction design includes 2-amino-6-methylpyridine as the amine to enhance the rates of multiple steps within the catalytic cycle while serving as an ammonia surrogate. These design principles point the way to the additions of N–H bonds of other reagents, as well as O–H and C–H bonds, across unactivated internal alkenes to streamline the synthesis of functional molecules from basic feedstocks.
DOI: 10.1038/s41586-020-2919-z
Source: https://www.nature.com/articles/s41586-020-2919-z