Frye Connor W, Egger Dominic T, Kounalis Errikos, Pearce Adam J, Cheng Yukun, Tonks Ian A
Department of Chemistry, University of Minnesota - Twin Cities 207 Pleasant St SE Minneapolis Minnesota 55455 USA
Chem Sci. 2021 Dec 27;13(5):1469-1477. doi: 10.1039/d1sc06111a. eCollection 2022 Feb 2.
α-Diimines are commonly used as supporting ligands for a variety of transition metal-catalyzed processes, most notably in α-olefin polymerization. They are also precursors to valuable synthetic targets, such as chiral 1,2-diamines. Their synthesis is usually performed through acid-catalyzed condensation of amines with α-diketones. Despite the simplicity of this approach, accessing unsymmetrical α-diimines is challenging. Herein, we report the Ti-mediated intermolecular diimination of alkynes to afford a variety of symmetrical and unsymmetrical α-diimines through the reaction of diazatitanacyclohexadiene intermediates with C-nitrosos. These diazatitanacycles can be readily accessed the multicomponent coupling of Ti[triple bond, length as m-dash]NR imidos with alkynes and nitriles. The formation of α-diimines is achieved through formal [4 + 2]-cycloaddition of the C-nitroso to the Ti and γ-carbon of the diazatitanacyclohexadiene followed by two subsequent cycloreversion steps to eliminate nitrile and afford the α-diimine and a Ti oxo.
α-二亚胺通常用作多种过渡金属催化过程的配体，最显著的是在α-烯烃聚合反应中。它们也是有价值的合成目标物的前体，如手性1,2-二胺。其合成通常通过胺与α-二酮的酸催化缩合来进行。尽管这种方法很简单，但合成不对称α-二亚胺具有挑战性。在此，我们报道了钛介导的炔烃分子间二亚胺化反应，通过二氮杂钛环己二烯中间体与C-亚硝基化合物反应，得到各种对称和不对称的α-二亚胺。这些二氮杂钛环可以通过Ti≡NR亚胺与炔烃和腈的多组分偶联反应轻松得到。α-二亚胺的形成是通过C-亚硝基与二氮杂钛环己二烯的钛和γ-碳进行形式上的[4 + 2]环加成，随后经过两个连续的环化逆转步骤，消除腈，得到α-二亚胺和一个钛氧代物。
