Department of Chemistry, Imperial College London, South Kensington, London SW7 2AZ, UK.
J Org Chem. 2013 Feb 1;78(3):844-54. doi: 10.1021/jo3027824. Epub 2013 Jan 23.
A series of novel, highly substituted N-PMP aziridines have been accessed in high yields by palladium-catalyzed cross-coupling of intact aziridines. The cross-coupling employed aryl bromides and tertiary organometallic aziridines, generated from sulfinylaziridines by sulfinyl-magnesium exchange and transmetalation to the aziridinylzinc with zinc chloride. A wide range of electron-rich and electron-poor aryl bromides were utilized to afford the functionalized aziridine products as single diastereoisomers with retention of configuration at the reacting center. Assessment of the reaction kinetics showed zero-order in both the aziridine species and the aryl bromide. This indicated that the rate-determining step was reductive elimination from the palladium(II) species bearing both the aziridine and aryl groups to form the hindered C-C bond. The intermediate aziridinylzinc species underwent a progressive, background degradation that led to a plateau in yield and afforded reduced yields in substrates with ortho-substituted aryl groups, which are less reactive due to the additional steric demands.
一系列新型的、高度取代的 N-PMP 氮丙啶可通过钯催化的完整氮丙啶的交叉偶联以高产率获得。该交叉偶联采用芳基溴化物和叔有机金属氮丙啶，由亚砜基氮丙啶通过亚砜基-镁交换和向氮丙啶基锌的转金属化并用氯化锌生成。广泛的富电子和缺电子芳基溴化物被用于提供作为单一非对映异构体的官能化氮丙啶产物，在反应中心保留构型。对反应动力学的评估表明，氮丙啶物种和芳基溴化物都是零级的。这表明速率决定步骤是从同时含有氮丙啶和芳基的钯(II)物种进行还原消除，形成受阻的 C-C 键。中间的氮丙啶基锌物种经历了渐进的、背景降解，导致产率达到平台期，并在具有邻位取代芳基的底物中得到较低的产率，这是由于额外的空间位阻导致反应性降低。
