Insertion of Nitriles into Zirconocene 1‐aza‐1,3‐diene Complexes: Chemoselective Synthesis of N–H and N‐Substituted Pyrroles

Abstract

The direct insertion of nitriles into zirconocene-1-aza-1,3-diene complexes provides an efficient, chemoselective, and controllable synthesis of N-H and N-substituted pyrroles upon acidic aqueous work-up. The outcome of the reaction (that is, the formation of N-H or N-substituted pyrroles) results from the different cyclization patterns, which depend on the relative stability and reactivity of the enamine-imine tautomers formed by hydrolysis of the diazazirconacycles.

Reactivity Study of Pyridyl‐Substituted 1‐Metalla‐2,5‐diaza‐cyclopenta‐2,4‐dienes of Group 4 Metallocenes

“…The solvents were purified with the Grubbs-type column system "Pure Solv MD-5" and dispensed into thick-walled glass Schlenk bombs equipped with Young-type Te flon valve stopcocks. Cp* 2 M(N=C(2-py)ÀC(2-py)=N) (1a:M= Ti, 2: M = Zr), [17] Cp* 2 Ti(N=C(Ph)ÀC(Ph)=N) (1b), [15a] [Cp* 2 Ti(N = C(m-C 6 H 4 )ÀC=N)] 3 (10), [16] [Cp* 2 Ti(N=C(m-C 6 H 3 N)ÀC=N)] 4 (11), [17] Cp* 2 Ti(h 2 -Me 3 SiC 2 SiMe 3 ) [37] and Cp* 2 Ti(N=C(2-Br-5-py)ÀC(2-Br-5-py)= N) (14) [17] were synthesised according to the published procedures. 2-Cyanopyridine, PhCH 2 ÀCN, benzonitrile and Me 2 SiCl 2 (all Sigma-Aldrich) were purified by distillation and stored under argon.…”

“…For the second case, the split‐off of [Cp′ 2 M] (M=Ti, Zr) from the nitrile complexes, two different reaction types were reported. The first is the hydrolysis, which was investigated for diverse compounds and afforded, for example, amines, azaindoles, ketones, pyrroles or other heterocycles . The second one is the exchange of [Cp′ 2 M] (M=Ti, Zr) by S 2 Cl 2 , PCl 3 or other electrophiles .…”

Plasma-Triggered CH4/NH3 Coupling Reaction for Direct Synthesis of Liquid Nitrogen-Containing Organic Chemicals

“…The C≡N bond as an important functional group has irreplaceable applications in medicine (anticancer drug, carew amine; antitumor medicine, stubborn azole; antidepressant drug, citalopram; and antipsychotic medicine, periciazine). 53−55 Chemicals containing C≡N bond also have great potential in the synthesis of organic compounds, such as pyrimidine, 56 tetrazene, 57 pyrrole, 58 amine, 59 imine, 60 and natural product molecules. 61 Therefore, this paper provides a potential carbon–nitrogen coupling path to form C≡N bond and functional chemicals containing C≡N bond, which are very significant in medicine and organic synthesis.…”

Group 4 Metallocene Mediated Homo- and Heterocoupling of Heteroaromatic Nitriles

“…Use of group 4 metallocenes is a well-established strategy that was used in the past to generate the products of olefin–olefin, olefin–alkyne, and alkyne–alkyne coupling via metallacycles . Coupling reactions of nitriles at zirconocene to furnish pyrroles, pyridines, pyridones, iminopyridines, or pyrimidines have been described . Together with Rosenthal, some of us have recently reported the first examples of nitrile–nitrile coupling at titanocene and zirconocene (Scheme a) .…”