Regioselective Synthesis of 6‐[Chloro(difluoro)methyl]salicylates by [3+3] Cyclocondensations of 1,3‐Bis(trimethylsilyloxy)buta‐1,3‐dienes with 1‐Chloro‐1,1‐difluoro‐4‐(trimethylsilyloxy)pent‐3‐en‐2‐one

The TiCl₄‐mediated [3+3] cyclocondensation of various 1,3‐bis(trimethylsilyloxy)buta‐1,3‐dienes with 1‐chloro‐1,1‐difluoro‐4‐(trimethylsilyloxy)pent‐3‐en‐2‐one provides a regioselective access to novel 6‐(chlorodifluoromethyl)salicylates (=6‐(chlorodifluoromethyl)‐2‐hydroxybenzoates) with very good regioselectivity. For selected products, it was demonstrated that the CF₂Cl group can be transformed to CF₂H and CF₂(Allyl) by free‐radical reactions.     

Cyclization vs. Elimination Reactions of 5‐Aryl‐5‐hydroxy 1,3‐Diones: One‐Pot Synthesis of 2‐Aryl‐2,3‐dihydro‐4H‐pyran‐4‐ones

2‐Aryl‐2,3‐dihydro‐4H‐pyran‐4‐ones were prepared in one step by cyclocondensation of 1,3‐diketone dianions with aldehydes. The use of HCl (10%) for the aqueous workup proved to be very important to avoid elimination reactions of the 5‐aryl‐5‐hydroxy 1,3‐diones formed as intermediates. The TiCl₄‐mediated cyclization of a 2‐aryl‐2,3‐dihydro‐4H‐pyran‐4‐one with 1,3‐silyloxybuta‐1,3‐diene resulted in cleavage of the pyranone moiety and formation of a highly functionalized benzene derivative.     

Low‐valent Titanium Induced Reductive Coupling of O‐Nitrophenylazide with Benzoyl Substituted Ketene Dithioacetals: a Novel Synthesis of 4‐Aryl‐2‐methylthio‐3Z7‐l,5‐benzodiazepines

Treated with the low‐valent titanium derived from TiCl₄/Sm system, o‐nitrophenylazide could produce the intermediate 2 in situ, which reacted with benzoyl substituted ketene dithioacetals to afford 4‐aryl‐2‐methylthio‐3H‐1,5‐benzodiazepines in good yields under mild and neutral conditions.     

Rapid ring‐opening polymerization of 1,4‐dioxan‐2‐one initiated by titanium alkoxides

Ring‐opening polymerization of 1,4‐dioxan‐2‐one in bulk was initiated by three titanium alkoxides, titanium dichlorodiisopropoxide (TiCl₂(OiPr)₂), titanium chlorotriisopropoxide (TiCl(OiPr)₃), and titanium tetraisopropoxide (Ti(OiPr)₄). The results indicate that the polymerization rate increased with number of OiPr groups in the initiator. High conversion of monomer (90%) and high molecular weight (11.9 × 10⁴ g/mol) of resulting polymer can be achieved in only 5 min at 60 °C with Ti(OiPr)₄ as an initiator. Analysis on nuclear magnetic resonance (NMR) spectra suggests the initiating sites for TiCl₂(OiPr)₂, TiCl(OiPr)₃, and Ti(OiPr)₄ to be 1.9, 2.6, and 3.8, respectively. Coordination‐insertion mechanism for the polymerization via cleavage of the acyl–oxygen bonds of the monomer was proved by NMR investigation. Kinetic studies indicate that polymerization initiated by Ti(OiPr)₄ followed a first‐order kinetics, with an apparent activation energy of 33.7 kJ/mol. It is noteworthy that this value is significantly lower than earlier reported values with other catalysts, namely La(OiPr)₃ (50.5 kJ/mol) and Sn(Oct)₂ (71.8 kJ/mol), which makes it an attractive catalyst for reactive extrusion polymerization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

A Facile One‐Step Synthesis of 2‐Arylindazoles via Reductive Cyclization of N‐(2‐nitroarylidene)amines

A mild and efficient synthesis of 2‐arylindazole derivatives via the reductive cyclization of nitro‐aryl substrates mediated by a low‐valent titanium reagent (TiCl₄/Sm/Et₃N) has been developed. The attractive features of the current method include an N–N bond formation and the selective reduction of the C = N bond and nitro group, both of which were easily achieved in one‐pot by controlling the pH of the reaction mixture.     

Lewis Acid‐Mediated Addition of Amino Acid‐Substituted α‐Allylsilanes to Aromatic Acetals

Unnatural amino acids extend the pharmacological formulator's toolkit. Strategies to prepare unnatural amino acid derivatives using Lewis acid‐activated allylsilane reactions are few. In this regard, we examined the utility of allylsilanes bearing an amino acid substituent in the reaction. Diastereoselective addition of methyl 2‐(N‐PG‐amino)‐3‐(trimethylsilyl)pent‐4‐enoate and methyl (E)‐2‐(N‐PG‐amino)‐3‐(trimethylsilyl)hex‐4‐enoate (PG=protecting group), 2 and 13 , respectively, to aromatic acetals in the presence of Lewis acids is described. Of those examined, TiCl₄ was found to be the most effective Lewis acid for promoting the addition. At least 1 equiv. of TiCl₄ was required to achieve high yields, whereas 2 equiv. of BF₃?OEt₂ were required for comparable outcomes. Excellent selectivity (>99% syn/anti) and high yield (up to 89%) were obtained with halo‐substituted aromatic acetals, while more electron‐rich electrophiles led to both lower yields and diastereoselectivities.     

Synthesis and Cytotoxicity Studies of New (Dimethylamino)‐Functionalised and 7‐Azaindole‐Substituted ‘Titanocene’ Anticancer Agents (7‐Azaindole=1H‐Pyrrolo[2,3‐b]pyridine)

From the carbolithiation of 1‐(cyclopenta‐2,4‐dien‐1‐ylidene)‐N,N‐dimethylmethanamine (=6‐(dimethylamino)fulvene; 3 ) and different lithiated azaindoles 2 (1‐methyl‐7‐azaindol‐2‐yl, 1‐[(diethylamino)methyl]‐7‐azaindol‐2‐yl, and 1‐(methoxymethyl)‐7‐azaindol‐2‐yl), the corresponding lithium cyclopentadienide intermediates 4a – 4c were formed (7‐azaindole=1H‐pyrrolo[2,3‐b]pyridine). The latter underwent a transmetallation reaction with TiCl₄ resulting in the (dimethylamino)‐functionalised ‘titanocenes’ 5a – 5c . When the ‘titanocenes’ 5a – 5c were tested against LLC‐PK cells, the IC₅₀ values obtained were of 8.8, 12, and 87 μM , respectively. The most cytotoxic ‘titanocene’, 5a , with an IC₅₀ value of 8.8 μM is nearly as cytotoxic as cis‐platin, which showed an IC₅₀ value of 3.3 μM when tested on the epithelial pig kidney LLC‐PK cell line, and ca. 200 times better than ‘titanocene dichloride’ itself.     

Die Kristallstrukturen von PPh4[MCl5(NCMe)] · MeCN (M = Ti,Zr), zwei Modifikationen von PPh4[TiCl5(NCMe)] und von cis‐TiCl4(NCMe)2 · MeCN

The Crystal Structures of PPh₄[MCl₅(NCMe)] · MeCN (M = Ti, Zr), two Modifications of PPh₄[TiCl₅(NCMe)] and of cis ‐TiCl₄(NCMe)₂ · MeCN The title compounds were obtained by reactions of TiCl₄ or ZrCl₄, respectively, with PPh₄Cl and acetonitrile in the presence of S₂Cl₂. PPh₄[TiCl₅(NCMe)] · MeCN is unstable and emanates the incorporated acetonitrile. PPh₄[TiCl₅(NCMe)] forms the two modifications aP114 and mP228, the latter being more stable. The crystal structures were determined by X‐ray diffraction. Triclinic PPh₄[TiCl₅(NCMe)]‐(aP114) crystallizes in a distorted variety at the tetragonal AsPh₄[RuNCl₄] type, i. e. with PPh₄⁺ ions that are piled to columns in the c direction; the [TiCl₅(NCMe)]^– ions are tilted vs. this direction and thus cause the symmetry reduction from P4/n to P1. PPh₄[TiCl₅(NCMe)] · MeCN and PPh₄[ZrCl₅(NCMe)] · MeCN also have the same packing principle as in AsPh₄[RuNCl₄] with a symmetry reduction from P4/n to P112₁/n and a doubled c axis. Instead, PPh₄[TiCl₅(NCMe)]‐(mP228) has a packing with (PPh₄⁺)₂ pairs. Orthorhombic TiCl₄(NCMe)₂ · MeCN contains molecules having two acetonitrile ligands attached to the Ti atom in a cis configuration.     

Titanium tetrachloride supported on atom transfer radical polymerized poly(methyl acrylate‐co‐1‐octene) as catalyst for ethylene polymerization

Ethylene polymerizations were performed using catalyst based on titanium tetrachloride (TiCl₄) supported on synthesized poly(methyl acrylate‐co‐1‐octene) (PMO). Three catalysts were synthesized by varying TiCl₄/PMO weight ratio in chlorobenzene resulting in incorporation of titanium in different percentage as determined by UV‐vis spectroscopy. The coordination of titanium with the copolymer matrix was confirmed by FTIR studies. The catalysts morphology as observed by SEM was found to be round shaped with even distributions of titanium and chlorine on the surface of catalyst. Their performance was evaluated for atmospheric polymerization of ethylene in n‐hexane using triethylaluminum as cocatalyst. Catalyst with titanium incorporation corresponding to 2.8 wt % showed maximum activity. Polyethylenes obtained were characterized for melting temperature, molecular weight, morphology and microstructure. The polymeric support utilized for TiCl₄ was synthesized using activators regenerated by electron transfer (ARGET) Atom Transfer Radical Polymerization (ATRP) of methyl acrylate (MA) and 1‐octene (Oct) with Cu(0)/CuBr₂/tris(2‐(dimethylamino)ethyl)amine (Me₆TREN) as catalyst and ethyl 2‐bromoisobutyrate (EBriB) as initiator at 80 °C. The copolymer poly(methyl acrylate‐1‐octene; PMO) obtained showed monomodal curve in Gel Permeation Chromatography (GPC) with polydispersity of 1.37 and copolymer composition (¹H NMR; F_MA) of 0.75. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7299–7309, 2008     

Low-valent Titanium Induced Intramolecular Reductive Coupling of Keto-enamines:A Facile Synthesis of 2,3,5-Trisubstituted Pyrroles

Promoted by low-valent titaium reagent which was generated in situ from Sm/TiCl4 system,keto-enamine derivatives underwent efficient intromolecular deoxygenative coupling reactions and afforded the corresponding 2,3,5-trisubstituted pyrroles in moderate to good yields under mild reaction conditions.     

An Expeditious Access to Enantiomerically Pure cis‐Dialkyl‐Substituted γ‐ and δ‐Lactones

A facile general route to enantiomerically pure 3,4‐cis‐dialkyl‐substituted γ‐lactones and 4,5‐cis‐dialkyl‐substituted δ‐lactones by TiCl₄‐mediated Evans asymmetric aldolization as the key step is exemplified by synthesis of cis‐(3R,4R)‐3‐methyldecan‐4‐olide and (4R,5R)‐aerangis lactone.     

Aza‐Belluš‐Claisen Rearrangement‐Enabled Synthesis of Racemic Tapentadol and Its Stereoisomers

A concise synthesis of racemic Tapentadol and its stereoisomers was presented. The key step was a TiCl₄·THF₂‐catalzyed aza‐Belluš‐Claisen rearrangement to create two vicinal tertiary carbon stereogenic centers. The subsequent reduction of amide and hydrogenation of alkene delivered Tapentadol and its stereoisomers. The current approach offers a practical synthetic route to access this class of pharmaceutically significant molecules.     

Amino‐ und halogenfunktionelle Siloxititane

Amino‐ and halofunctional Siloxititanes Amino‐di‐tert‐butylsilanol reacts with tetrabutoxititane in a molar ratio of 2:1 to give di‐n‐butoxi(bis(di‐tert‐butyl‐n‐butoxi)siloxi)titane, (C₄H₉OSi(CMe₃)₂‐O)₂Ti(OC₄H₉)₂ ( 1 ), and lithium‐di‐tert‐butylchlorosilanolate in a molar ratio of 3:1 to give n‐butoxi(tris(di‐tert‐butyl‐n‐butoxi)siloxi)titane, (H₉C₄OSi(CMe₃)₂‐O)₃TiOC₄H₉ ( 2 ). The amino‐di‐tert‐butylsilanol substitutes the four chloroatoms of TiCl₄ in the presence of triethylamine as HCl‐acceptor. The tetrakis(amino‐di‐tert‐butyl)siloxititane ( 3 ) is formed. The lithium salt of di‐tert‐butylfluorosilanol reacts with TiCl₄ in a molar ratio of 2:1 to give 1, 1, 3, 3‐tetra‐tert‐butyl‐1‐fluoro‐3‐trichlorotitoxi‐1, 3‐disiloxane, FSi(CMe₃)₂‐O‐Si(CMe₃)₂‐O‐TiCl₃ ( 4 ). In the reaction of di‐tert‐butyl‐chlorosilanol and TiCl₄, the anion [chlorosiloxi‐octa(tri‐μ²‐chlorotitanate)]^— ( 5 ) with protonated diethylether as counterion is obtained by using diethylether as HCl‐acceptor. The crystal structure determinations of 3 and 5 are reported.     

2‐(Diphenylphosphinoylmethyl)pyrrole–2‐(diphenylphosphinomethyl)pyrrole (0.43/0.57) and tetrachlorido(5‐diphenylphosphinomethyl‐2H‐pyrrole‐κ2N,P)titanium(IV)

The title phosphine oxide–phosphine, 0.43C₁₇H₁₆NOP·0.57C₁₇H₁₆NP, (I)/(II), was obtained as a 0.861 (6):1.139 (6) cocrystallized mixture. Hydrogen bonding between the two constituents leads to the formation of 2:2 solid‐state assemblies. Instead of forming the expected simple N,P‐chelated system via loss of the N‐bound H atom, reaction of 2‐(diphenylphosphinomethyl)pyrrole, (II), with TiCl₄ leads to the formation of the title titanium(IV) complex, [TiCl₄(C₁₇H₁₆NP)], (IV), containing a rearranged neutral ligand in which the N‐bound H atom moves to one of the pyrrole C atoms, giving a partially unsaturated ring.     

Syntheses of 4‐(5‐oxo‐1,2,4‐triazol‐3‐yl)‐sydnones and 4‐(4‐arylamino‐5‐oxo‐1,2,4‐triazol‐3‐yl)‐sydnones from Sydnone Derivatives and Their Fragments

4‐(5‐oxo‐1,2,4‐triazol‐3‐yl)‐sydnones 11 and 4‐(4‐arylamino‐5‐oxo‐1,2,4‐triazol‐3‐yl)‐sydnones 13 have been obtained from a‐chloroformylarylhydrazine hydrochloride 2 . Moreover, the intermediates, including 3, 4 , 9 and 10 , in this study are synthetically informative and valuable. It is also noteworthy that three reactants, 1, 2 and sydnonecarbaldehydes, were prepared from sydnone derivatives and their fragments. The oxidative cyclizations of sydnonecarbaldehyde semicarbazones 9 and carbazones 10 with two different oxidizing agents (Cu(ClO₄)₂ and Fe(ClO₄)₃) have been extensively examined. The reaction time and the yields of cyclizations were affected by the substituents of semicarbazones 9 and carbazones 10.     

Efficient terpolymerization of ethylene and styrene with α‐olefins by aryloxo‐modified half‐titanocene‐based catalysts and cocatalyst systems

Aryloxo‐modified half‐titanocenes, Cp′TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) [Cp′ = Cp* ( 1 ), ^tBuC₅H₄ ( 2 )], catalyze terpolymerization of ethylene and styrene with α‐olefin (1‐hexene and 1‐decene) efficiently in the presence of cocatalyst, affording high‐molecular‐weight polymers with unimodal distributions (compositions). Efficient comonomer incorporations have been achieved by these catalysts. The content of each comonomer (α‐olefin, styrene, etc.) could be controlled by varying the comonomer concentration charged, and resonances ascribed to styrene and α‐olefin repeated insertion were negligible. The terpolymerization with p‐methylstyrene (p‐MS) in place of styrene also proceeded in the presence of [PhN(H)Me₂][B(C₆F₅)₄] and AlⁱBu₃ cocatalyst, and p‐MS was incorporated in an efficient matter, affording high‐molecular‐weight polymers with uniform molecular weight distributions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2565–2574     

The discovery and progress of MgCl2‐supported TiCl4 catalysts

Polyolefins represented by polyethylene (PE) and polypropylene (PP) are indispensable materials in our daily lives. TiCl₃ catalysts, established by Ziegler and Natta in the 1950s, led to the births of the polyolefin industries. However, the activities and stereospecificities of the TiCl₃ catalysts were so low that steps for removing catalyst residues and low stereoregular PP were needed in the production of PE and PP. Our discovery of MgCl₂‐supported TiCl₄ catalysts led to more than 100 times higher activities and extremely high stereospecificities, which enabled us to dispense with the steps for the removals, meaning the process innovation. Furthermore, they narrowed the molecular weight and composition distributions of PE and PP, enabling us to control the polymer structures precisely and create such new products as very low density PE or heat‐sealable film at low temperature. The typical example of the product innovations by the combination of the high stereospecificity and the narrowed composition distribution is high‐performance impact copolymer used for an automobile bumper that used to be made of metal. These process and product innovations established these polyolefin industries. The latest MgCl₂‐supported TiCl₄ catalyst is very close to perfect control of isotactic PP structure and is expected to bring about further innovations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1–8, 2004     

A two‐dimensional cadmium(II) coordination polymer constructed from 4‐carboxy‐1‐(4‐carboxylatobenzyl)‐2‐propyl‐1H‐imidazole‐5‐carboxylate and 1‐(4‐carboxylatobenzyl)‐2‐propyl‐1H‐imidazole‐4‐carboxylate ligands

Crystals of poly[[aqua[μ₃‐4‐carboxy‐1‐(4‐carboxylatobenzyl)‐2‐propyl‐1H‐imidazole‐5‐carboxylato‐κ⁵O¹O^1′:N³,O⁴:O⁵][μ₄‐1‐(4‐carboxylatobenzyl)‐2‐propyl‐1H‐imidazole‐4‐carboxylato‐κ⁷N³,O⁴:O⁴,O^4′:O¹,O^1′:O¹]cadmium(II)] monohydrate], {[Cd₂(C₁₅H₁₄N₂O₄)(C₁₆H₁₄N₂O₆)(H₂O)]·H₂O}_n or {[Cd₂(Hcpimda)(cpima)(H₂O)]·H₂O}_n, (I), were obtained from 1‐(4‐carboxybenzyl)‐2‐propyl‐1H‐imidazole‐4,5‐dicarboxylic acid (H₃cpimda) and cadmium(II) chloride under hydrothermal conditions. The structure indicates that in‐situ decarboxylation of H₃cpimda occurred during the synthesis process. The asymmetric unit consists of two Cd²⁺ centres, one 4‐carboxy‐1‐(4‐carboxylatobenzyl)‐2‐propyl‐1H‐imidazole‐5‐carboxylate (Hcpimda²⁻) anion, one 1‐(4‐carboxylatobenzyl)‐2‐propyl‐1H‐imidazole‐4‐carboxylate (cpima²⁻) anion, one coordinated water molecule and one lattice water molecule. One Cd²⁺ centre, i.e. Cd1, is hexacoordinated and displays a slightly distorted octahedral CdN₂O₄ geometry. The other Cd centre, i.e. Cd2, is coordinated by seven O atoms originating from one Hcpimda²⁻ ligand and three cpima²⁻ ligands. This Cd²⁺ centre can be described as having a distorted capped octahedral coordination geometry. Two carboxylate groups of the benzoate moieties of two cpima²⁻ ligands bridge between Cd2 centres to generate [Cd₂O₂] units, which are further linked by two cpima²⁻ ligands to produce one‐dimensional (1D) infinite chains based around large 26‐membered rings. Meanwhile, adjacent Cd1 centres are linked by Hcpimda²⁻ ligands to generate 1D zigzag chains. The two types of chains are linked through a μ₂‐η² bidentate bridging mode from an O atom of an imidazole carboxylate unit of cpima²⁻ to give a two‐dimensional (2D) coordination polymer. The simplified 2D net structure can be described as a 3,6‐coordinated net which has a (4³)₂(4⁶.6⁶.8³) topology. Furthermore, the FT–IR spectroscopic properties, photoluminescence properties, powder X‐ray diffraction (PXRD) pattern and thermogravimetric behaviour of the polymer have been investigated.     

Low‐Valent Titanium Induced Simultaneous Reduction of Nitro Group and S?S Bond in Nitrodisulfides: A Facile Synthesis of 2H‐1,4‐Benzothiazines

The simultaneous reduction of nitro group and S? S bond in nitrodisulfides by TiCl₄/Sm system led to the active intermediates 2, which were “living” double‐anions in situ and reacted smoothly with ω‐bromoketones to afford the desired 2/7–1,4‐benzothiazines in good yields under mild and neutral conditions.     

A Convenient Synthesis of 2,3‐Dihydro‐4H‐thiopyrano[2,3‐b]‐, ‐[2,3‐c]‐, or ‐[3,2‐c]pyridin‐4‐ones by the Reaction of the Corresponding 1‐(Chloropyridinyl)alk‐2‐en‐1‐ones with NaSH

2,3‐Dihydro‐4H‐thiopyrano[2,3‐b]pyridin‐4‐ones 4 were prepared by a three‐step sequence from commercially available 2‐chloropyridine ( 1 ). Thus, successive treatment of 1 with ⁱPr₂NLi (LDA) and α,β‐unsaturated aldehydes gave 1‐(2‐chloropyridin‐3‐yl)alk‐2‐en‐1‐ols 2 , which were oxidized with MnO₂ to 1‐(2‐chloropyridin‐3‐yl)alk‐2‐en‐1‐ones 3 . The reactions of 3 with NaSH?n H₂O proceeded smoothly at 0° in DMF to provide the desired thiopyranopyridinones. Similarly, 2,3‐dihydro‐4H‐thiopyrano[2,3‐c]pyridin‐4‐ones 8 and 2,3‐dihydro‐4H‐thiopyrano[3,2‐c]pyridin‐4‐ones 12 were obtained starting from 3‐chloropyridine ( 5 ) and 4‐chloropyridine ( 9 ), respectively.