10.1021/ol0502026
The study by Scott T. Handy and Duncan Omune investigates the reductive cyclization of tethered bis-enones with one-carbon tethers, focusing on the influence of reaction conditions and α-substitution on the cyclization pathway. They found that the cyclization products, either pinacol or hydrodimerization-type, are highly dependent on these factors. The researchers synthesized three cyclization substrates and explored their reductive cyclization under electrochemical conditions and using samarium diiodide. They observed that electrochemical conditions favored pinacol-type products, while samarium diiodide favored reductive cyclization products. The study suggests that chelation and steric effects play a crucial role in determining the cyclization pathway, with Lewis acidic metals promoting pinacol formation and non-chelatable metals favoring reductive cyclization. This mechanistic understanding was further supported by experiments using magnesium in methanol, which resulted in pinacol products. The findings highlight the importance of reaction conditions in controlling the cyclization outcome and provide insights into the mechanism of reductive cyclization reactions.
10.1016/j.tet.2004.03.049
The research presents a highly efficient synthesis method for lennoxamine and related isoindolobenzazepines, which are alkaloids derived from the Chilean plant Berberis darwinii. The study focuses on an improved approach to synthesizing these compounds through intramolecular condensation of aldehyde isoindolones under basic conditions, followed by catalytic hydrogenation of the resulting dehydroisoindolobenzazepines. Key reactants in the synthesis include aldehyde isoindolones, which are derived from the alkylation-acylation of arylethylamines with ethyl 2-chloromethylbenzoate derivatives. The synthesis involves formylation using dichloromethyl methyl ether and titanium tetrachloride, and the cyclization is performed in refluxing methanolic KOH. The dehydro intermediates are then catalytically hydrogenated to yield the final products. Analyses of the synthesized compounds were conducted using techniques such as 1H and 13C NMR spectroscopy, mass spectrometry, and infrared spectroscopy, with purification through column chromatography and recrystallization from methanol. The research also discusses the structural requirements for successful synthesis, such as the facilitative role of methoxy groups in the cyclization process.
10.1016/0040-4020(86)80014-X
The research focuses on the synthesis of oxygen-containing heterocycles with a vinylidene exocyclic group, specifically vinylidyne-5 dioxanes-1,3, through organosilicon chemistry. The purpose of the study is to develop a regiospecific method for the preparation of these compounds using α-silyloxypropargyltrimethylsilanes, which react with aliphatic aldehydes in a one-pot reaction. The researchers found that this method effectively yields a variety of alkyl-substituted 5-vinylidene-1,3-dioxanes with good yields and purity. The chemicals used in the process include α-silyloxypropargyltrimethylsilanes, aliphatic aldehydes with primary or secondary alkyl groups, and Lewis acids such as TiCl4 and BF3.O(C2H5)2 as catalysts. The study concludes that the presence of a Lewis acid facilitates the regiospecific reaction of α-silyloxypropargyltrimethylsilanes with aliphatic aldehydes, leading to the formation of diversely substituted vinylidyne-5 dioxanes-1,3 in a single step and with good yields.
10.1055/s-1989-27134
The research focuses on the exploration of a new route to synthesize disubstituted 2'-hydroxypropiophenones using titanium tetrachloride induced Fries rearrangement. The purpose of this study was to develop a convenient method for the synthesis of hindered dialkyl 2'-hydroxypropiophenones, which are important intermediates for pharmaceutical applications. The researchers utilized various dialkylphenyl propionates and phenols as starting materials, with titanium tetrachloride and aluminum chloride serving as catalysts to achieve the rearrangement and subsequent elimination reactions. The conclusions drawn from the study indicate that the sequential use of these reagents allowed for the synthesis of previously unknown 3',6'- and 5',6'-dialkyl-2-hydroxypropiophenones, demonstrating the effectiveness of the method in producing these compounds. The research also highlighted the importance of understanding the electronic and steric effects on the reaction outcomes, as well as the role of the catalysts in influencing the reaction pathways.
10.1246/cl.1983.97
The research aims to develop a stereocontrolled synthesis method for 2-methyl-2-alkenenitriles through a diastereoselective aldol-type reaction. The study utilizes C-methyl-C,N-bis(trimethylsilyl)ketenimine (1) and various aldehydes, activated by a mixture of TiCl4 and Ti(O-iPr)4, to achieve this goal. The researchers found that the yield and diastereoselectivity of the reaction product 2 were significantly improved by using a modified titanium reagent composed of TiCl4 and Ti(O-iPr)4 in a 1/3 ratio. This mixture forms a mixed ligand titanium compound, TiCl(O-iPr)3, which enhances the reaction's stereoselectivity. The study concludes that the substituents on the α-carbon of the aldehydes and the ratio of TiCl4 to Ti(O-iPr)4 play crucial roles in controlling the stereochemistry of the products. Nonbranched aldehydes lead to (Z)-2-alkenenitriles, while branched aldehydes result in (E)-2-alkenenitriles under the optimized conditions. The results suggest that the aggregation of ketenimine and aldehydes around the titanium atom is key to controlling the stereochemical outcome, providing a new and effective route for the stereoselective synthesis of 2-methyl-2-alkenenitriles.
10.1016/j.tetlet.2010.06.037
The study presents a simplified and scalable procedure for the TiCl4-promoted aldol reaction, a method for forming carbon-carbon bonds widely used in natural product and pharmaceutical synthesis. The researchers compared the conventional method of adding TiCl4, DIPEA, and aldehydes sequentially to a new method where TiCl4 is added last to a solution of the substrates and DIPEA in CH2Cl2. The new procedure yielded cleaner reactions at higher temperatures and was reproducible on a large scale, though it lacked stereoselectivity. Key chemicals used were TiCl4 as the promoter, (i-Pr)2NEt (DIPEA) as the base, and various aldehydes and carbonyl compounds as substrates for the aldol reaction. The purpose of these chemicals was to facilitate the formation of the desired aldol products, which are intermediates in the synthesis of endothelin receptor antagonists.
10.1016/j.bmcl.2004.11.046
The study focuses on the regioselective synthesis of modified proanthocyanidins by introducing acyl substituents at the C-8 position of (+)-catechin, leading to the creation of various catechin derivatives. These derivatives were utilized for further synthesis of modified proanthocyanidins, with a particular emphasis on the synthesis of a new 3-O-4 ether-linked procyanidin-like derivative. Key chemicals used in the study include tetra-O-benzyl catechin, penta-O-benzyl catechin, trifluoroacetic anhydride, and titanium tetrachloride (TiCl4) as a catalyst. These chemicals served various purposes, such as starting materials for the synthesis, reagents for acylation and electrophilic addition reactions, and a catalyst for the selective condensation reaction that led to the formation of the ether-linked procyanidin-like derivative. The study aimed to investigate the influence of substitution patterns on the behavior of these compounds in Lewis acid-catalyzed synthesis of naturally occurring procyanidins and to develop a new methodology for managing regiochemical features related to the dimerization reaction of flavan-3-ol monomers.
10.1055/s-0028-1088043
The study presents the first synthesis of 5-cyanosalicylates through formal [3+3] cyclocondensations of 1,3-bis(silyloxy)-1,3-butadienes with 3-ethoxy- and 3-silyloxy-2-cyano-2-en-1-ones. The research focuses on the preparation of functionalized benzonitriles, which are important building blocks for fine chemical synthesis and are found in various dyes, pharmaceuticals, agrochemicals, herbicides, and pesticides. The study details the synthesis process, which involves the use of titanium tetrachloride as a mediator for the cyclization reaction, leading to the formation of 5-cyanosalicylates with excellent regioselectivity. These compounds are not readily available through other methods, making this research significant for the synthesis of pharmacologically active products. The study also discusses the optimization of reaction conditions and provides a comprehensive analysis of the synthesized products using spectroscopic methods and X-ray crystal structure analyses.
10.1016/S0022-328X(00)89067-1
The research focuses on the synthesis and molecular structures of chiral ansa-titanocene derivatives with bridged tetrahydroindenyl ligands. The purpose of this study was to develop easily accessible synthetic routes for these stereorigid, chiral organometallic compounds, which have potential applications as chiral hydride- or alkyl-transfer agents. The researchers synthesized racemic ethylene-bis(4,5,6,7-tetrahydro-1-indenyl)titanium dichloride and determined its molecular structure, along with that of its meso-isomer and a binaphtholate complex of the (S,S)-enantiomer. They found that the meso-isomer could be converted to the racemic form through exposure to light, a process likely involving a reversible homolytic metal-ring separation. The chiral ansa-titanocene framework was found to be resistant to racemization during ligand exchange. Key chemicals used in the process included 1,2-bis(3-indenyl)ethane, titanium tetrachloride, (S)-(-)-binaphthol, and various solvents and reagents for purification and chromatographic separation.
10.1016/j.tetlet.2008.07.146
The study investigates the synthesis of diethyl c-hydroxy-a,a-difluoromethylenephosphonates through the ring-opening reactions of epoxides. Key chemicals involved include titanium tetrachloride (TiCl4), which acts as a Lewis acid to promote the ring-opening of epoxides, and lithium diethyl difluoromethylenephosphonate, which serves as a nucleophile. The study explores the reactivity of various epoxides, such as propylene oxide, 1,2-butene oxide, styrene oxide, and cyclohexene oxide, with these reagents. The reactions are regioselective, favoring attack at the less hindered site of the epoxide ring. The study also examines the use of Grignard reagents, which act as both nucleophiles and Lewis acids, leading to the formation of halohydrins. The synthesized compounds have potential applications in the design of non-hydrolyzable analogues of biologically active phosphate esters and as substrates for certain enzymes.
F, 
Xi, 
C
F:Flammable;
