Alkylative Reduction of Titanium(IV) Isopropoxide with EtMgBr: Convenient Method for the Generation of Subvalent Titanium Alkoxide Reagents and their Reactivity in Pinacol Coupling Reactions

Abstract

The composition of the gaseous products from the reaction of Ti(IV) isopropoxide with ethylmagnesium bromide in diethyl ether evidences the formation of subvalent titanium isopropoxide species in various oxidation states depending on relative amounts of the reactants. Reaction of titanium(IV) isopropoxide with one equivalent of the Grignard reagent gives presumably titanium(III) isopropoxide. The latter is generated as a result of disproportionation of starting Ti(IV) species and titanium(II) isopropoxideethene complex which is formed as a result of ethane extrusion from diethyltitanium(IV) isopropoxide. Titanium(III) isopropoxide prepared by this way transforms the aldehydes and the aromatic ketones into the corresponding pinacols in good yields.

Visible-Light-Promoted Reduction of Epoxides, Hydroxysulfonates, and Halohydrines with Alkyltitanium Alkoxides

“…Being readily available and nontoxic, titanium reagents and catalysts have been employed in remarkably diverse organic transformations including oxidation, reduction, and C–C bond forming reactions. − Low valent titanium species, especially Ti III compounds, are powerful reducing agents capable of reacting with carbonyl, imine, oxime, epoxide, acylaziridine, halide, hydroxyl, oxazoline, and other functional groups (Scheme A). − These reagents are air-sensitive and typically prepared in situ by the reduction of an available Ti IV compound with a suitable reductant such as K, Zn, Mn, or Mg metals or a Grignard reagent. Recently, Ti III/IV catalysis was successfully merged with photoredox catalysis, where reduction of Ti IV was achieved by the oxidative quenching of a photocatalyst .…”