In Situ Catalyst Generation and Benchtop-Compatible Entry Points for Ti^II/Ti^IV Redox Catalytic Reactions

Abstract

The development of several in situ generated catalyst systems for Ti-catalyzed oxidative nitrene transfer reactions is reported. The simplest and widely applicable catalyst system, TiCl 4 (THF) 2 / Zn 0 , can be set up on the benchtop under air. This system uses commercially available reagents and can be used as an entry point for Ti II /Ti IV multicomponent redox reactions for the synthesis of pyrroles, α,γ-unsaturated imines, α,β-unsaturated imines, cyclopropylimines, and arenes.

Multicomponent Pyrazole Synthesis from Alkynes, Nitriles, and Titanium Imido Complexes via Oxidatively Induced N–N Bond Coupling

“…This scope demonstrates that multisubstituted pyrazoles can be accessed directly and generally in a single step through multicomponent coupling of Ti imidos, while avoiding prerequisite hydrazine or hydrazine-derived coupling partners. Conveniently, [py 2 TiCl 2 (NPh)] 2 and derivatives thereof can be prepared in a single pot from TiCl 4 (THF) 2 , and we have recently demonstrated benchtop-compatible Ti imido generation . Thus, access to these multicomponent coupling reactions does not require specialized equipment or protocols.…”

α-Diimine synthesis via titanium-mediated multicomponent diimination of alkynes with C-nitrosos

“…We have previously shown that this strategy is a benchtop-compatible approach to other Ti oxidative amination reactions. 54 This one-pot approach facilitates the in situ formation of diazatitanacycle intermediates such as 1 without the need for specialized equipment, making the synthesis of both α-diimines and pyrazoles 32 more operationally simple.…”

Multicomponent syntheses of 5- and 6-membered aromatic heterocycles using group 4–8 transition metal catalysts

“…3), such as CAT3. The proposed catalytic cycle for this process, determined through combined experimental and computational studies, [35][36][37][38] is highlighted in Fig. 3.…”