On the Mechanism and Kinetics of Radical Reactions of Epoxyketones and Epoxynitriles Induced by Titanocene Chloride

Synthesis of Succinonitrile Derivatives by Homocoupling from Cyanohydrin Derivatives with a Low-Valent Titanium Reagent

A method is described for synthesizing succinonitrile derivatives bearing alkyl or aryl substituents from cyanohydrin derivatives using low-valent titanium. The active species in this reaction is proposed to be a resonance hybrid of the Ti^IV nitrile enolate and Ti^III alkyl radical.

Titanium(III)-Catalyzed Reductive Decyanation of Geminal Dinitriles by a Non-Free-Radical Mechanism

A titanium-catalyzed mono-decyanation of geminal dinitriles is reported. The reaction proceeds under mild conditions, tolerates numerous functional groups, and can be applied to quaternary malononitriles. A corresponding desulfonylation is demonstrated as well. Mechanistic experiments support a catalyst-controlled cleavage without the formation of free radicals, which is in sharp contrast to traditional stoichiometric radical decyanations. The involvement of two TiIII species in the C-C cleavage is proposed, and the beneficial role of added ZnCl2 and 2,4,6-collidine hydrochloride is investigated.

Total Synthesis of (±)-Marsupellins A and B via Acetoxymarsupellone Using an Intramolecular Reductive Cyclization of Epoxycyanohydrin Derivative with Cp2TiI

The first total synthesis of C3- and C9-oxidized ent-longipinane-type sesquiterpenoids containing acetoxymarsupellone, marsupellins A and B, has been accomplished. This unique core common to C3- and C9-oxidized ent-longipinane-type sesquiterpenoids was constructed via a new intramolecular reductive cyclization reaction of an epoxycyanohydrin derivative using Cp₂TiI.

Photoredox Catalysis: Construction of Polyheterocycles via Alkoxycarbonylation/Addition/Cyclization Sequence

A novel visible-light-induced cascade reaction for the preparation of ester-functionalized polyheterocycles was developed under metal-free conditions, which was initiated by an intermolecular radical addition to a carbon-carbon double bond of N-arylacrylamide derivatives using alkyl carbazate as the ester source followed by cyano-mediated cyclization. The desired phenanthridine derivative products were isolated in moderate to high yields with broad substrate scope.

An efficient synthesis of sulfonated quinoline diones by copper catalyzed sulfonylation of activated alkenes with sulfonylhydrazides

A novel and highly efficient cascade synthesis of sulfonated quinoline dione derivatives from N-(2-cyanoaryl) methylacrylamides and sulfonylhydrazides in good yields is described.

Copper-catalyzed cascade addition/cyclization: highly efficient access to phosphonylated quinoline-2,4(1H,3H)-diones

A novel Cu-catalyzed addition/cyclization cascade of o-cyanoarylacrylamide has been developed for the synthesis of various phosphonylated quinoline-2,4(1H,3H)-diones.

Reductive umpolung reactions with low-valent titanium catalysts

The coupling of similarly polarized carbon fragments can be achieved by a reductive umpolung strategy. This gives access to compounds with functional groups in even bond distances, which are difficult to synthesize by other means. Low-valent titanium catalysts enable such couplings under mild conditions. This account covers the recent progress on this topic with a focus on the development of cross-selective coupling reactions and stereoselective examples.

Titanocene(III)-promoted Barbier-type crotylation of carbonyl compounds

A mild, highly regio- and stereoselective method for the crotylation of aldehydes and ketones mediated/catalyzed by titanocene(III) is described. Optimized conditions permit the selective generation of γ-adducts in high yields together with high stereoselectivity, with a predominance of anti stereoisomers.

Catalysis via homolytic substitutions with C-O and Ti-O bonds: oxidative additions and reductive eliminations in single electron steps

In a combined theoretical and experimental study, an efficient catalytic reaction featuring epoxide opening and tetrahydrofuran formation through homolytic substitution reactions at C-O and Ti-O bonds was devised. The performance of these two key steps of the catalytic cycle was studied and could be adjusted by modifying the electronic properties of the catalysts through introduction of electron-donating or -withdrawing substituents to the titanocene catalysts. By regarding both steps as single electron versions of oxidative addition and reductive elimination, a mechanism-based platform for the design of catalysts and reagents for electron transfer reactions evolved that opens broad perspectives for further investigations.

Titanocene(III)-catalyzed formation of indolines and azaindolines

Reductive cyclization of epoxides tethered to substituted anilines and aminopyridines in the presence of 3 mol % of titanocene dichloride and stoichiometric manganese metal promotes a radical annulation to form 3,3-disubstituted indolines and azaindolines.