Presence Of TiCl4 Research Articles

A practical approach to the degradation of polychlorinated biphenyls in transformer oil

A practical and efficient disposal method for hydrodechlorination of polychlorinated biphenyls (PCBs) in transformer oil is reported. Transformer oil containing PCBs was treated by nanometric sodium hydride (nano-NaH) and transition metal catalysts. High destruction and removal efficiency (89.8%) can be attained by nano-NaH alone under mild conditions. The process exhibits apparent characteristics of a first order reaction. The reductive ability of nano-NaH was enhanced by the addition of transition metal catalysts. In the presence of TiCl 4, 99.9% PCBs was hydrodechlorinated. The complex reducing reagents, Ni(OAc) 2 + i-PrONa, show extra hydrodechlorinating activity for di-chlorinated biphenyls.

Lewis Acid Mediated Reductive Ring Opening of 2-Methoxyethylidene Acetals: A New Approach to 2-Methoxyethyl (MOE) Ethers ofcis-Diols

The reductive opening of 2-methoxyethylidene acetals of vicinal diols in uridine and 1,4-anhydro-d-ribitol in the presence of TiCl4 and Et3SiH was investigated. The 3′-O-(2-methoxyethyl) ether of uridine and the 2′-O-(2-methoxyethyl) ether of 1,4-an­hydro-d-ribitol were isolated and characterized. The results were rationalized based on coordination effects involving proximal substituents.

A substrate controlled, very highly diastereoselective Morita–Baylis–Hillman reaction: a remote activation of the diastereofacial selectivity in the synthesis of C-3-branched deoxysugars

The Morita–Baylis–Hillman (MBH) reaction of p-nitrobenzaldehyde with C (6) acyl protected enuloside 1 in the presence of TiCl 4/TBAI yielded highly diastereoenriched C-3-branched deoxysugar derivative or MBH adduct 1′ a in high yield, while reactions of unprotected enuloside 2a and C (6) alkyl protected enulosides 2d– e with p-nitrobenzaldehyde under the same conditions afforded the adducts 2′ a and 2′ d– e , respectively, in low yield with moderate selectivity. Several representative aromatic and aliphatic aldehydes were selected to undergo MBH reaction with 1 to give their respective adducts in very good yield with a very high diastereoselectivity. A plausible mechanism based on the assumption of a Zimmerman–Traxler-type transition state was proposed to explain the excellent selectivity observed with adducts derived from 1 . The synthetic application of these adducts were shown by their stereoselective reduction to corresponding threo isomers in very good yield.

Diastereoselective addition of organozinc reagents to 2-alkyl-3-(arylsulfanyl)propanals

The preparation of compounds incorporating the 3-hydroxy-2-methyl-1-alkyl moiety of high diastereomeric purity is described. Such compounds can serve as potential building blocks for the preparation of several kinds of natural products. Diastereoselective synthesis of two potential pine sawfly pheromone components, one the pure racemic threo-isomer of 3-methylpentadecan-2-ol and the other the racemic erythro-isomer of 3-methyltridecan-2-ol are described. The diastereoselective addition of R 2Zn (R=Me, Et and n-Bu) to several 2-alkyl-3-(arylsulfanyl)propanals in the presence of a Lewis acid and CH 2Cl 2 as solvent was studied. An excellent diastereomeric ratio (95/5 anti-Cram/Cram) was obtained with 2-[(phenylsulfanyl)methyl]pentanal, 2-[(phenylsulfanyl)methyl]decanal and 2-[(phenylsulfanyl)methyl]dodecanal and Me 2Zn in the presence of TiCl 4.

C‐Acylation of 2‐Methylfuran and Thiophene Using N‐Acylbenzotriazoles.

Reactions of 2-methylfuran and thiophene with readily available N-acylbenzotriazoles (RCOBt, where R = 4-tolyl, 4-methoxyphenyl, benzyl, 4-nitrophenyl, 4-diethylaminophenyl, 2-pyridyl and 1-naphthyl) in the presence of TiCl 4 or ZnBr 2 produced 2-methyl-4-acylfurans 2a-e and 2-acylthiophenes 3a-f in average yields of 54 % and 75 %, respectively. Literature yields for the preparation of the same compounds are significantly lower.

Metal Chelation in Asymmetric Diels—Alder Reaction (II).

AbstractFor Abstract see ChemInform Abstract in Full Text.

Novel π-Conjugated Nano-Supramolecules Having Fine-Controlled Metal-Assembling Functions

Abstract Dendritic and cyclic polyphenylazomethines (DPA and CPA) were exploited as π-conjugated polymer ligands having novel topological structures. DPAs were synthesized by the convergent method via dehydration in the presence of TiCl4. DPA G4 molecules have a sphere-like structure with a 2.3-nm diameter, and they are regularly assembled without deformation of the molecule on a plate, as observed by means of GPC, molecular modeling, TEM, AFM, and π–A measurements. The stepwise radial complexation in DPAs with SnCl2 was observed as a stepwise shift in the isosbestic point in the UV–vis spectra; this conclusion was further supported by TEM, NMR, and shell-selective reduction (SSR) of the imines. The order of complexation among the shells permits control by the introduction of electron-withdrawing groups to the DPA structure. CPAn-ab and CPAn-aabb (designated as CPAX-Y where X and Y are the degree of polymerization and whether the polymerization was AB- or AABB-type, respectively) was synthesized via dehydration in the presence of TiCl4, TiCl4(THF)2 or p-toluenesulfonic acid (PTS). The unique structures of CPAn-ab and CPAn-aabb: triangle, square, or oblong, and their regular molecular-packing were revealed by NMR, MD calculations, and X-ray crystal analysis. CPAn-aabb shows reversible redox functions by protic acid doping, unlike conventional polyphenylazomethine (PPA).

Enantioselective total synthesis of (+)-brefeldin A and 7-epi-brefeldin A.

A convergent enantioselective route to brefeldin A (BFA) and 7-epi-BFA was developed. The key C-4/C-5 chiral centers were established by using chiral auxiliary induced intermolecular asymmetric aldolization in the presence of TiCl(4) and TMEDA. The results with the thiazolidinethione/TiCl(4) mediated intermolecular asymmetric aldolization added some new information about the scope and limitations to the existing knowledge of that type of reactions (which so far was essentially limited to the reactions with N-propionyl thiazolidinethiones). During the course a method for protecting the liable aldol hydroxyl groups by using inexpensive TBSCl in DMF with 2,6-lutidine as the base was developed to replace the otherwise unavoidable TBSOTf procedure. Due to the excessive steric hindrance, removal of the auxiliary was much more difficult than most literature cases. Cleavage of the oxazolidinone by reduction was almost impossible. The thiazolidinethione auxiliary was relatively easier to remove. However, several reactions reported for facile removal of thiazolidinethione auxiliaries in the literature still failed. Reductive removal of the thiazolidinethione auxiliary was most effectively realized with LiBH(4) in diethyl ether in the presence of 1 equiv of MeOH (a modification of a literature procedure for removal of oxazolidinone auxiliaries in less hindered substrates). Apart from the auxiliary removal, oxidation of the alcohol into aldehyde and the deprotection of the dithiolane protecting group were also rather difficult in the present context. A range of methods were screened before final solutions were found. The five-membered ring was constructed by employing an intramolecular Mukaiyama reaction after many attempts with the intramolecular aldolization under a variety of conditions failed. The rate of elimination of the alkoxyl to form the alpha,beta-double bond of the key intermediate cyclopentenone 49 with DBU was highly solvent dependent (very sluggish in CH(2)Cl(2) but rather fast in MeOH). Introduction of the lower chain (which was synthesized by using a Jacobsen KHR to establish the C-15 chirality) was achieved through a Michael addition similar to the precedents in the literature. It has not been noticed before that the yield of this Michael reaction could be dramatically raised by using 3 equiv of the copper-lithium reagent 55. Reduction of the C-7 carbonyl was apparently more difficult than similar cases in the literature. After examination of many reagents under various conditions, it was found that the best reagent for yielding the alpha-isomer was (S)-2-methyl-CBS-borolidine/BH(3) and that for the beta-isomer was L-Selectride. The alpha- and beta-isomers were then further elaborated into (+)-brefeldin A and 7-epi-BFA, respectively. An unexpected yet very interesting solubility difference between BFA and 7-epi-BFA was also observed.

Metal Chelation in Asymmetric Diels-Alder Reaction (II)

Diels-Alder cycloadditions of chiral dieno-philes with cyclopentadiene proceed with diastereofacialselectivity, giving either endo-R or endo-S compounds as amajor component, depending on Lewis acids used.In the reaction, the inverse asymmetric induction has beenobserved by the use of either monovalent Lewis acids ordivalent Lewis acids. The reaction of the acrylate of ( S)-ethyllactate with cyclopentadiene proceeded with 86% endo-Sselectivity in the presence of TiCl

Synthesis of [11C]/(13C)amines via carbonylation followed by reductive amination.

Twelve 11C-labelled amines were prepared via 11C-carbonylation followed by reductive amination. The 11C-carbonylation was performed in the presence of tetrakis(triphenylphosphine)palladium using aryl iodides or aryl triflates, [11C]carbon monoxide and phenyl-/methylboronic acid. The [11C]ketones formed in this step were then transformed directly into amines by reductive amination using different amines in the presence of TiCl4 and NaBH3CN. The 11C-labelled amines were obtained with decay-corrected radiochemical yields in the range 2-78%. The radiochemical purity of the isolated products exceeded 98%. (13C)Benzhydryl-phenyl-amine was synthesised and analysed by NMR spectroscopy for confirmation of the labelling position. Specific radioactivity was determined for the same compound. The reference compounds were prepared by reductive amination of ketones using conventional reaction conditions and three of the compounds were novel. The presented approach is a new method for the synthesis of [11C]/(13C)amines.

Dendritic polyphenylazomethines: Synthesis, structure, and metal-assembling function

Abstract Dendritic polyphenylazomethines (DPAs) were synthesized as novel topological polymer ligands with pi-conjugated structures by the convergent method via dehydration of aromatic ketones with aromatic amines in the presence of TiCl4. DPA G4 molecules are revealed to have a sphere-like structure with a 2.3-nm diameter and are regularly assembled without deformation of the molecule on a plate as observed by means of gel permeation chromatography (GPC), molecular modeling, transmission electron microscopy (TEM), atomic force microscopy (AFM), and pi-A measurements. The stepwise radial complexation in DPAs with SnCl2 was observed as a stepwise shift in the isosbestic point in the UV-vis spectra. The number of added equivalents of SnCl2 required to induce a shift was in agreement with the number of imine groups present in the different shells of the DPAs. These spectral changes suggest that the complexation is proceeding in a stepwise fashion from the core imines to the terminal imines of the DPAs, which was further supported by shell-selective reduction (SSR) of the imines.

A novel arylation of arylacetic acid esters using tertiary arylamines and TiCl 4

The reactions of arylacetic acid esters with tertiary arylamines in the presence of TiCl 4 give α-arylated products in 65–90% yields, as well as 10–20% yields of the corresponding benzidines.

Thio Diels–Alder reactions of α,β-unsaturated 1,3-oxathiolanes with aliphatic olefins and 1,3-dienes

A series of α,β-unsaturated 1,3-oxathiolanes reacted with aliphatic olefins such as norbornene and with various 1,3-dienes in the presence of TiCl 4 leading to dihydrothiapyrans, via a cycloaddition-type reaction. The unsaturated oxathiolanes acted as masked heterodienes in this thio Diels–Alder reaction.

Intermediates in the synthesis of nitrogen heterocycles: addition of acylated camphorsultams to nitroalkenes

Abstract Reaction of acylated camphorsultam 7 with nitroalkenes in the presence of TiCl4 and Et3N gave addition products in good yields (>70%) and with excellent stereocontrol. Addition of propionylated camphorsultam 15 to nitrostyrene gave the addition product 16 in which two new asymmetric centres were created, the stereochemical outcome of the reaction was confirmed by X-ray cystallography.

Chalcogenide—Lewis Acid Mediated Reactions of Electron‐Deficient Alkynes with Aldehydes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of novel phenylazomethine derivatives as a multi‐dentate ligand for advanced metal‐organic hybride nano‐materials

AbstractOligophenylazomethines (OPAs) and the aniline‐capped OPAs were synthesized via dehydration of 4‐aminobenzophenone in the presence of TiCl4 as a Lewis acid. TiCl4 acts as an excellent dehydration agent for formation of the C=N bond. OPAs have some isomers, which are based on the E/Z conformation of the azomethine moieties. Novel cyclic molecules, the cyclic phenylazomethine trimer (CPA3‐ab) derivatives, were synthesized via the dehydration of the 4‐aminobenzophenone. The yields of the macrocycles were enhanced to over 90% by induction of the bulky α‐substituent to the substrate. The highly preferential formation of novel aabb‐type phenylazo‐methine macrocycles was also achieved. The resulting CPA6‐aabb has unique structure based on the E/Z conformation of the azomethine bonds, the extremely regular molecular‐packing state. The novel dendritic phenylazomethines(DPAs), were synthesized by the convergent method. The DPAs have a high solubility unlike the conventional linear polyphenylazomethines. The tin chloride complexed to the imine groups of DPAs in a stepwise fashion. The complexation occurs in the order of 1st, 2nd, 3rd, and 4th layers of DPA G4.

α,β‐Unsaturated 1,3‐Oxathiolanes as Masked Heterodienes in the Thio Diels—Alder Reaction with Styrene Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Chalcogenide-Lewis acid mediated reactions of electron-deficient alkynes with aldehydes.

Reactions of but-3-yn-2-one (2) with aldehydes 1 in the presence of a Lewis acid and dimethyl sulfide (3 a) predominantly gave (E)-alpha-(halomethylene)aldols 4-5 in high yields, while reactions of methyl propiolate (6 a) mainly afforded (Z)-3-halogeno-2-(hydroxymethyl)acrylates 7-8 in low to moderate yields. A reaction of dimethyl acetylenedicarboxylate (10) with 1 a in the presence of TiCl(4) and 1,1,3,3-tetramethylthiourea (3 c) produced maleate (E)-11 (40 %) and butenolide 12 (40 %). When a reaction of 6 a with 1 a was carried out in the presence of TiBr(4) and 3 a (0.2 equiv) at -20 degrees C for 60 h, 3-(methylthio)-2-(hydroxyalkyl)acrylate 9 a was obtained in an 8 % yield. Experiments were conducted in order to elucidate the formation mechanism of 9 a, and it was made clear that 9 a was formed via the processes of the Michael addition of sulfide 3 a to alkynoate 6 a and an aldol reaction with 1 a and demethylation.

Medium-sized cyclophanes. Part 62:1 Formylation of anti-[n.2]metacyclophanes — Through-space electronic interactions between two benzene rings

Formylation of anti-[n.2]metacyclophanes (1) (n = 2, 3, 4) with dichloromethyl methyl ether in the presence of TiCl4 occurred selectively at para-position to the internal methyl substituents of anti-[n.2]metacyclophanes. Similar reaction of anti-5,13-di-tert-butyl-8,16-dimethyl[2.2]metacyclophane (6a) with dichloromethyl methyl ether in the presence of TiCl4 led to ipso-formylation at the tert-butyl group to give anti-5-tert-butyl-13-formyl-8,16-dimethyl[2.2]-meta cyclophane (7a) as well as the corresponding 2,7-di-tert-butyl-trans-10b,10c-dimethyl-10b,10c-dihydropyrene (10), anti-5-tert-butyl-8,16-dimethyl-13-(3-methyl-1-butene-2-yl)[2.2]metacyclophane (8), and anti-5,13-di-tert-butyl-exo-1-hydroxy-8,16-dimethyl[2.2]metacyclophane (9) depending on the reaction conditions. The higher yield of ipso-formylated product is obtained in the presence of AlCl3 MeNO2 in 80% yield along with anti-5-tert-butyl-8,16-dimethyl-13-(3-methyl-1-butene-2-yl)[2.2]metacyclophane (13). Thus, the yield of ipso-formylation at the tert-butyl group of 6a was strongly affected by the activity of the formylation catalyst. Interestingly, in the formylation of anti-6,14-di-tert-butyl-9,17-dimethyl[3.2]metacyclophane (6b) under the same reaction conditions, syn-6,14-di-tert-butyl-7-formyl-9,17-dimethyl[3.2]metacyclophane (14b) was obtained in 40% yield arising from the anti-syn-ring inversion of the formylation intermediate along with ipso-formylation product 7b in 42% yield. In the formylation of anti-[4.2] meta cyclophane (6c) only the mono-ipso-formylated product 7c was obtained in 92% yield. The formation of a two-fold ipso-formation product, i.e., anti-5,13-diformyl-8,16-dimethyl[2.2]metacyclophane (3a), was not observed under the reaction conditions used. The mechanism of the ipso-formation as well as the formation of the present novel reaction products 8 and 9 is also discussed. Key words: cyclophanes, strained molecules, electrophilic aromatic substitution, ipso-formylation, σ-complex intermediates, through-space electronic interactions.

One‐Pot Aza‐Baylis—Hillman Reactions of Arylaldehydes and Diphenylphosphinamide with Methyl Vinyl Ketone in the Presence of TiCl4, PPh3, and Et3N.

AbstractFor Abstract see ChemInform Abstract in Full Text.