Selective Incorporation of Primary Amines into a Trizirconium Imido System and Catalyic Cyclization of Aminoalkynes

Abstract

The trinuclear zirconium imido complex [{LZr(NMe)}] (2, L = CMeCHCHN) was synthesized by amine elimination between Zr(NMe) and endo-olefinic isomers of (tetramethylcyclopentadienyl)ethanamine (LH) (1). To study the fundamental reactivity of the trizirconium system, reactions of 2 with primary amines were examined. Selective incorporations of the primary amines were observed, depending on steric and electronic natures of the amine substrates. The amine-incorporated complexes [(LZrNHR)(LHZrNHR)(LHZr)(μ-NHR)(μ-NR)] (3, R = Pr, Et), [(LZrNHR)(LHZr)(μ-NR)] (4, R = Pr, i-Bu), [(LZr)(LZrNMe)(μ-NR)] (5, R = neo-Pen), and [(LZr)(LZrNHAr)(LHZr)(μ-NAr)] (6, Ar = Ph, CH-4-Br, CH-4-OMe) were structurally characterized by NMR and XRD analysis and showed several coordination modes of the substrate nitrogen ligands: i.e., terminal amides, bridging amides, and bridging imides but not terminal imides. Thermolysis of a mixture of 3 and 4 led to C-H bond activation, giving rise to the zirconaaziridines [{LZr(η-NCHR)}(LZr)(LHZr)(μ-NHCHR)] (12, R = Et, Me). Complex 2 proved to be a competent precatalyst in the hydroamination of the aminoalkynes (HNCHCRCHC≡CR) (13, R = H, R = Bu, Ph, t-Bu; 14, R = Me, R = Et, Ph). Stoichiometric or semicatalytic reactions of 2 and the aminoalkynes were studied to explore the reactivity of in situ formed Zr species.

Synthesis of Nitrogen-Containing Heterocyclic Scaffolds through Sequential Reactions of Aminoalkynes with Carbonyls

“…The Brønsted acid-promoted reaction of β-(2-aminophenyl)-α,β-ynones with ketones was expanded to activated carbonyl compounds, such as β-ketoesters and β-diketones. The carbonyl group at position 3 of the quinoline nucleus could further react with the other keto functionality in the alkyl substituent at position 4, generating an additional [ 3 , 4 ]-fused six-membered ring whose structure depends on the type of β-dicarbonyl compound used. Indeed, for β-ketoesters, a thorough screening of reaction conditions revealed that catalytic amounts of p -TsOH·H 2 O were sufficient to efficiently promote a cascade double cyclization leading to 4 H -pyrano [3,4- c ]quinoline-4-one derivatives 77 .…”

“…Their behavior changes by activation of the C-C triple bond by a metal catalyst. Various biologically important nitrogen heterocycles were directly synthesized in an easy way by means of intramolecular hydroamination of aminoalkynes in the presence of several transition metal as well as lanthanide catalysts [ 4 , 5 ]. The aptitude to form π- and σ-complexes can help in the choice of catalysts for the desired transformations when bi- or polyfunctional substrates are involved [ 6 ].…”

“…, x FOR PEER REVIEW 40 of 87 . Indium-catalyzed multicomponent synthesis of 9H-benzo[f]imidazo [1,2-d][1,2,3]triazolo [1,5a][1,4]diazepines 37.…”

Synthesis of Nitrogen Containing Heterocyclic Scaffolds through Sequential Reactions of Aminoalkynes with Carbonyls

“…The carbonyl group at position 3 of the quinoline nucleus could further react with the other keto functionality in the alkyl substituent at position 4, generating an additional [3,4]fused six-membered ring whose structure depends on the type of β-dicarbonyl compound used. Indeed, for β-ketoesters, a thorough screening of reaction conditions revealed that catalytic amounts of p-TsOH•H 2 O were sufficient to efficiently promote a cascade double cyclization leading to 4H-pyrano [3,4-c]quinoline-4-one derivatives 77.…”

“…Their behavior changes by activation of the C-C triple bond by a metal catalyst. Various biologically important nitrogen heterocycles were directly synthesized in an easy way by means of intramolecular hydroamination of aminoalkynes in the presence of several transition metal as well as lanthanide catalysts [4,5]. The aptitude to form πand σ-complexes can help in the choice of catalysts for the desired transformations when bi-or polyfunctional substrates are involved [6].…”