Titanocene(III) chloride mediated radical-induced synthesis of 3,4-dihydroisocoumarins: synthesis of (±)-hydrangenol, (±)-phyllodulcin, (±)-macrophyllol and (±)-thunberginol G

A radical-promoted synthesis of 3,4-dihydroisocoumarins has been achieved in moderate to good yields using titanocene(III) chloride (Cp₂TiCl) as the radical initiator. The total synthesis of four naturally occurring dihydrocoumarins hydrangenol, phyllodulcin, macrophyllol and thunberginol G has been accomplished using the radical technology. Cp₂TiCl was prepared in situ from commercially available titanocene dichloride (Cp₂TiCl₂) and Zn-dust in THF under argon.     

Titanocene(III) chloride mediated radical induced asymmetric synthesis of α-methylene bis-γ-butyrolactone

Asymmetric synthesis of α-methylene bis-γ-butyrolactone has been synthesized using titanocene(III) chloride as a radical source. Titanocene(III) chloride (Cp₂TiCl) was prepared in situ from commercially available titanocene dichloride (Cp₂TiCl₂) and zinc dust in THF.     

Titanocene (III) chloride mediated radical induced synthesis of (−)-methylenolactocin and (−)-protolichesterinic acid

Enantioselective synthesis of two anti-tumor antibiotics, (−)-methylenolactocin and (−)-protolichesterinic acid, has been achieved through titanocene(III) chloride mediated radical cyclization reaction starting from commercially available d-mannitol. Titanocene(III) chloride (Cp₂TiCl) was prepared in situ from commercially available titanocene dichloride (Cp₂TiCl₂) and zinc dust in THF.     

Titanocene(III) mediated 8-endo radical cyclizations for the synthesis of eight-membered cyclic ethers

Titanocene(III) chloride (Cp₂TiCl) mediated 8-endo radical cyclizations towards the synthesis of eight-membered cyclic ethers have been described. Titanocene(III) chloride was prepared in situ from commercially available titanocene dichloride (Cp₂TiCl₂) and activated zinc dust in THF.     

Free radical-promoted conjugate addition of activated bromo compounds using titanocene(III) chloride as the radical initiator

Free radical-promoted conjugate addition of activated bromo compounds to α,β-unsaturated ketones and reactive α,β-unsaturated esters has been described using titanocene(III) chloride (Cp₂TiCl) as the radical initiator. Cp₂TiCl was prepared in situ from commercially available Cp₂TiCl₂ and activated zinc dust in THF.     

Titanocene(III) mediated radical cyclizations of epoxides for the synthesis of medium-sized cyclic ethers

Titanocene(III) chloride (Cp₂TiCl) mediated 7-exo and 8-endo radical cyclizations of epoxides towards the synthesis of 7- and 8-membered cyclic ethers have been described. Titanocene(III) chloride was prepared in situ from commercially available titanocene dichloride (Cp₂TiCl₂) and activated zinc dust in THF.     

Titanocene(III) mediated radical cyclization of α-bromo carbonyl compounds: synthesis of tri-substituted tetrahydrofurans

A novel and efficient methodology has been developed for the construction of synthetically important tri-substituted tetrahydrofuran derivatives from bromo-alkenes and bromo-alkynes by radical cyclization reactions using the radical initiator Cp₂TiCl, generated in situ from commercially available titanocene dichloride and Zn dust in tetrahydrofuran under argon.     

Radical promoted cyclizations of aromatic carbonyl compounds to benzopyrans using titanocene(III) chloride

Aromatic carbonyl compounds undergo smooth intramolecular radical cyclization with alkenes or alkynes using titanocene(III) chloride to furnish the corresponding benzopyrans. The radical initiator, Cp₂TiCl, was prepared in situ from commercially available titanocene dichloride (Cp₂TiCl₂) and zinc dust in THF under argon.     

Titanocene(III) chloride mediated radical-induced one-pot synthesis of α-methylene-γ-butyrolactones

A simple and efficient methodology has been developed for the one-pot preparation of α-methylene-γ-butyrolactones by free-radical induced Barbier-type reaction of methyl 2-(bromomethyl)acrylate and aldehydes followed by in situ lactonization. The radical initiator titanocene(III) chloride (Cp₂TiCl) was easily generated in situ from commercially available Cp₂TiCl₂ and activated zinc dust in THF. Ketones remained unaffected under the reaction conditions.     

Employing (half-)titanocene complexes as initiators for the synthesis of end-functionalized polylactides by coordination polymerization

Seven (half-)titanocene alkoxide complexes, [Cp₂TiCl(OEt)], [Cp₂TiCl(O-2-Bu)], [Cp₂TiCl(OCH₂CF₂CF₂H)], [CpTiCl₂(OEt)], [CpTiCl₂(O-(S)-2-Bu)], [CpTiCl₂(OCH₂CF₃)], and [Cp₂TiCl(OCH₂CF₃)], were synthesized and employed in lactide coordination polymerization. These organotitanium (IV) compounds proved to be very efficient initiators for the ring-opening polymerization of enantiomeric l -lactide and racemic mixture of rac-lactide, leading to end-functionalized polymers. Kinetic studies illustrated that these compounds produce well-defined polymers in a controlled manner. This was further demonstrated by synthesizing poly(l -lactide-b-hexyl isocyanate) diblock copolymer. The effect of the alkoxy end groups on the thermal behavior of the polymers was also studied by thermogravimetric analysis and differential scanning calorimetry. The polymers were characterized using size exclusion chromatography and proton nuclear magnetic resonance spectroscopy. The optical properties of the diblock copolymer were also investigated. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2192–2202     

Interaction of dicyclopentadienyltitanium dichloride with bis(triethylgermyl)-cadmium and -mercury

The reaction of dicyclopentadienyltitanium dichloride with bis(triethylgermyl)mercury in benzene solution at 20° yields metallic mercury quantitatively, titanocene monochloride and triethylchlorogermane. The reaction of dicyclopentadienyltitanium dichloride with bis(triethylgermyl)cadmium leads to the formation of a complex of the following general composition: [Cp₂TiCl₂ - Cd(GeEt₃)₂]. The reactivity of this complex has been studied: in toluene solution at 20° it decomposes slowly to yield metallic cadmium, triethylchlorogermane and Cp₂TiCl(GeEt₃).     

Studies on titanium organic compounds: VIII. Mechanism of vinyl polymerization in the presence of titanocene dichloride

The mechanism of catalytic polymerization of acrylonitrile in the presence of titanocene dichloride under light have been investigated by UV, NMR and ESR spectroscopy. Results of photochemical reaction monitored by UV and NMR showed that titanocene dichloride (Cp₂TiCl₂) in dimethyl sulfoxide system can be decomposed by light irradiation to give cyclopentadiene. ESR studies show that cyclopentadienyl free radical in photopolymerization system of Cp₂TiCl₂-acrylonitrile can be trapped by two kinds of spin trapping agents, phenyl-N-tert-butylnitrone and 2-methyl-2-nitrosopropane, respectively. Therefore, the radical mechanism of catalytic polymerization of acrylonitrile in the presence of Cp₂TiCl₂ under light is further confirmed.     

Titanocene(III) chloride mediated radical induced allylation of aldimines: formal synthesis of C-linked 4'-deoxy aza-disaccharide

Titanocene(III) chloride (Cp(2)TiCl) mediated radical induced allylation of aldimines for the preparation of homoallyl amines is described. The radical was generated from the allyl bromide using Cp(2)TiCl as the radical source. Formal synthesis of C(4)-C(5')-linked 4'-deoxy aza-disaccharide is demonstrated and a study toward the bicyclic skeleton of alkaloids was also accomplished. The radical initiator Cp(2)TiCl was prepared in situ from commercially available titanocene dichloride (Cp(2)TiCl(2)) and Zn dust in THF under argon.     

Mechanism of the controlled radical polymerization of styrene and methyl methacrylate in the presence of dicyclopentadienyltitanium dichloride

The mechanism of the controlled radical polymerization of styrene and methyl methacrylate in the presence of dicyclopentadienyltitanium dichloride (Cp₂TiCl₂) was studied using quantum chemical calculations and electron spin resonance spectroscopy. It was established that the reduction of Cp₂TiCl₂ to Cp₂TiCl during the macromolecule synthesis occurs through the living polymerization mechanism, which adjusts the growth of a polymeric chain. The geometrical structures of the molecular complexes between a growing macroradical and Cp₂TiCl₂ and transition states of radical inhibition steps were optimized and the thermodynamic and kinetic parameters of the elementary reactions were estimated for several feasible directions of the process. On this basis, the observed kinetic features of vinylic monomer polymerization with participation of organic compounds of titanium are discussed. Copyright © 2004 John Wiley & Sons, Ltd.     

An ESR study on the reaction between dicarbonyl titanocene and aryl-tin halides

The oxidation elimination reaction between dicarbonyl titanocene and aryltin halides was studied by means of paramagnetic resonance spectroscopy. The radical intermediates containing Ti(III) were discovered from the ESR spectra to be (Cp₂TiSnAr_nX_3-n), Cp₂Ti(CO)X, and Cp₂TiX, and a radical mechanism for the reaction is proposed. © 1996 John Wiley & Sons, Inc.     

Titanocen-cyandithioformiat-Komplexe

The reaction of titanocene dichloride,Cp ₂TiCl₂ (Cp=⁵-C₅H₅), with one or two equivalents of sodium cyanodithioformate affords the new mono- or bis(dithiocarboxylato) derivativesCp ₂TiCl(S₂CCN) (1) andCp ₂Ti(S₂CCN)₂ (2). Elimination of sulfur converts2 into the metallacyclicCp ₂TiS₂C₂(CN)₂ (3), which does not react with the diene isoprene, but can be reconverted into the appropriate titanocene dihalides by chlorine or bromine.

     

Synthese und Struktur eines neuen Bis[(trimethylphosphan)titanocen]-Komplexes mit einer verbrückenden C2-Einheit

Bis(trimethylphosphane)titanocene ( 1 ) reacts with 2-methylene-1,1-diphenylcyclopropane ( 2 ) to give red crystalline (η²-2-methylene-1,1-diphenylcyclopropane)(trimethylphosphane)titanocene ( 3 ). In solution complex 3 degrades smoothly to form the new Cp₂Ti(PMe₃) – C₂ – Ti(PMe₃)Cp₂ complex 4 , the crystal structure of which has been elucidated by an X-ray analysis.     

Development of novel MgCl2 supported catalyst with trivalent titanocene complex of CP2TiCl2AlCl2 for propylene polymerization

Three kinds of MgCl₂‐supported trivalent titanocene catalyst (Cat. 1: Cp₂TiCl₂AlCl₂/MgCl₂, Cat. 2: CpCp*TiCl/MgCl₂, Cat. 3: Cp₂TiCl/MgCl₂) were prepared and tested for propylene polymerization. It was found that Cat. 1, combined with ordinary alkylaluminum as cocatalyst, produced PP containing 31.8 wt % of isotactic PP in fairly good yield. On the other hand, Cats. 2 and 3 hardly showed any activity. The effects of diisopropyldimethoxysilane (DIPDMS) on isospecificity of the Cat. 1 also were investigated. The isotactic index (I.I.) of PP was improved drastically by the addition of DIPDMS as external donor and reached the value as high as 98.4%, even in the absence of any internal donors. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3355–3359, 2000     

An electrochemical study of (η-C5H5)2Ti(NCS)2

The reduction of titanocene dithiocyanate in various solvents has been examined using the techniques of polarography, voltammetry, controlled potential electrolysis and cyclic voltammetry. In THF and CH₂Cl₂, Cp₂Ti(NCS)₂ undergoes successive one-electron transfer reactions, and by using a combination of electrochemical and EPR techniques it has been possible to confirm the stability of [Cp₂Ti(NCS)₂]^? in these solvents. In DMF, however, an irreversible dimerization follows the first electron transfer.     

Addition of polyfluoroalkyl halides to 1-octeneinitiated by dichlorobis(π-cyclopentadienyl)-titanium and iron

Addition of various polyfluoroalkyl halides including 1,2-dihalopolyfluoroalkanes to1-octene is effected by using a catalytic amount of Cp_2TiCl_2(IV) and iron powder to give 1:1 adductsin excellent yields. The reaction is performed in EtOH or THF. A Cp_2TiCl(Ⅲ) mediatedradical mechanism is proposed. Radical reactivity of polyfluoroalkanes toward 1-octene was foundto be --CF_2I> -CF_2Br >-CF_2CCl_3.