Olefin metathesis in room temperature ionic liquids using imidazolium-tagged ruthenium complexes

New recyclable imidazolium-tagged ruthenium catalysts have been developed to perform olefin metathesis in room temperature ionic liquids (RTILs). High level of recyclability combined with a high reactivity were obtained in the ring-closing metathesis (RCM) of a variety of di- or tri-substituted and/or oxygen-containing dienes. Extremely low residual ruthenium levels were detected in the RCM products (average of 7.3 ppm per run). Several examples of olefin cross-metathesis (CM) have been also studied.     

Effect of anionic ion-pairing reagent hydrophobicity on selectivity of peptide separations by reversed-phase liquid chromatography

Despite the continuing dominance of trifluoroacetic acid (TFA) as the anionic ion-pairing reagent of choice for peptide separations by reversed-phase high-performance liquid chromatography (RP-HPLC), we believe that a step-by-step approach to re-examining the relative efficacy of TFA compared to other ion-pairing reagents is worthwhile, particularly for the design of separation protocols for complex peptide mixtures, e.g., in proteomics applications. Thus, we applied RP-HPLC in the presence of different concentrations of anionic ion-pairing reagents - phosphoric acid, TFA, pentafluoropropionic acid (PFPA) and heptafluorobutyric acid (HFBA)--to a mixture of three groups of four 10-residue peptides, these groups containing peptides of +1, +3 or +5 net charge. Overall separation of the 12-peptide mixture improved with increasing reagent hydrophobicity (phosphate- < TFA- < PFPA- < HFBA-) and/or concentration of the anion, with reagent hydrophobicity having a considerably more pronounced effect than reagent concentration. HFBA, in particular, achieved an excellent separation at a concentration of just 10 mM, whereby the peptides were separated by charged groups (+1 < +3 < +5) and hydrophobicity within these groups. There was an essentially equal effect of reagent hydrophobicity and concentration on each positive charge of the peptides, a useful observation for prediction of the effect of varying counterion concentration hydrophobicity and/or concentration during optimization of peptide purification protocols. Peak widths were greater for the more highly charged peptides, although these could be decreased significantly by raising the acid concentration; concomitantly, peptide resolution increased with increasing concentration of ion-pairing reagent.     

Reaction of octafluorocyclopentene with various carbon nucleophiles

The treatment of octafluorocyclopentene with organolithium reagents gave the corresponding symmetrical disubstituted perfluorocyclopentenes in good to high yields. The reaction with Grignard reagents led to the monosubstituted perfluorocyclopentenes, which were subjected to the further nucleophilic substitution reaction using another Grignard or aryllithium reagents, unsymmetrical disubstituted perfluorocyclopentenes being obtained in high yields.     

Changes in the reactivity of the fluorescent reagents carbazole-9-carbonyl chloride and 9-carbazolylacetic acid in the presence of cyclodextrins

Carbazole-9-carbonyl chloride (C9CC) and 9-carbazolylacetic acid (9CAA) were selected as model fluorescent reagents. The effect of different chemically modified cyclodextrins (CDs) added to the aqueous solutions of these reagents was studied in water and in buffered aqueous solutions at pH 4.5 and 8.8. The CDs employed were 2-hydroxypropyl-β-cyclodextrin (HP-βCD), 2,3-di-O-methyl-β-cyclodextrin (DM-βCD) and 2,3,6-tri-O-methyl-β-cyclodextrin (TM-βCD). The inclusion of these reagents inside the cavities of the CDs was verified and this process can affect the derivatization reaction because CDs can modify the reactivity of the guest molecules. The basic conditions necessary for the derivatization reaction between C9CC and amines lead to the formation of carbazole anion through hydrolysis followed by decarboxylation. In the presence of CDs, the hydrolysis-decarboxylation of carbazole-9-carbonyl chloride is faster than in buffered aqueous homogeneous solutions. The behaviour observed for these reagents in aqueous solutions of CDs was compared to the one observed in basic ethanolic solutions. These changes are particularly noticeable in the case of 2,3-di-O-methyl-β-CD and 2-hydroxypropyl-β-CD. The characteristics of the fluorescent reagents are compared to carbazole and 9-methylcarbazole as model compounds. This paper was presented at XIIIth International Cyclodextrin Symposium. Torino, Italy, May 14–17, 2006.     

The first example of γ-chloromagnesio γ-lactones: their generation from γ-tolylsulfinyl γ-lactones with isopropylmagnesium chloride, stability, and reaction with electrophiles

The treatment of γ-lactones having a sulfinyl group at the γ-position, which were synthesized from 1-chlorovinyl p-tolyl sulfoxides with lithium enolate of carboxylic esters, with isopropyl magnesium chloride in THF at −78 °C gave γ-chloromagnesio γ-lactones by the sulfoxide-magnesium exchange reaction in high yields. The generated γ-chloromagnesio γ-lactones were found to be stable at below −50 °C for at least 2 h. The reaction of these γ-chloromagnesio γ-lactones with electrophiles and the stereochemistry of the reactions were investigated.     

Elution of Cationic Species with/without Ion Pair Reagents from Polar Stationary Phases via SFC

Traditionally, the application of supercritical fluid chromatography has been limited to compounds of relatively low polarity. Thus, we report here that one secondary amine and two quaternary amine salts were successfully eluted from a Deltabond Cyano-bonded silica column with the addition of sodium alkylsulfonate to the methanol-modified, carbon dioxide-based mobile phase. A possible ion-pairing interaction between the positively charged analytes and the anionic part of the sulfonate additive has been proposed. In another set of experiments, the three amine salts readily eluted from both Ethyl-pyridine-bonded silica and Amino-bonded silica phases without the need of additive although the peak shapes were less than desirable. The addition of sulfonate salt to the mobile phase again sharpened the peaks. In the presence of a mixture of methanol and CO₂, we suggest that these stationary phases are positively charged. We describe here also for the first time the employment of a strong silica-based anion exchange (SAX) column for supercritical fluid separation of cationic species. Two elution mechanisms were proposed for the three amine salts depending upon whether the ionic additive was incorporated into the mobile phase. Separation as the ion-pair was proposed with an ionic additive in the mobile phase; whereas separation of the intact amine salt from the positively charged basic stationary phases was suggested to be operational without the ionic additive.     

Synthesis of cetyltrimethylammonium tribromide (CTMATB) and its application in the selective oxidation of sulfides to sulfoxides

The bright yellow crystalline cetyltrimethylammonium tribromide (CTMATB) reagent has been synthesized from the reaction of CTMAB and KBr with H₂MoO₄·H₂O, H₂O₂ and H₂SO₄ in the molar ratio 1:2:0.01:4:0.93. CTMATB selectively oxidizes a variety of dialkyl and alkyl aryl sulfides to the corresponding sulfoxides in high yields under mild conditions.     

Hydroarylation of alkynes and alkenes through alumina-sulfuric acid catalyzed regioselective CC bond formation

A highly atom-efficient synthetic protocol for hydroarylation of terminal-aryl alkynes and styrene through the regioselective CC bond formation via the electrophilic addition of naphthols and substituted phenols has been developed using alumina-sulfuric acid as a heterogeneous supported solid acid catalyst. This methodology shows excellent regioselectivity and affords the desired product in good to excellent yield. The heterogeneous catalyst can also be recycled efficiently without much loss of activity.     

硅胶固载化─（Lewis）酸催化剂的研究Ⅰ．硅胶固载化─四氯化钛复合物催化体系

以硅胶球为基质键合γ－ＧＯＰＳ并各接枝上具有络合功能的三种配体，邻位氨基吡啶、间酰氨基吡啶及对酰氨基吡啶，再和ＴｉＣｌ＿４络合成固载化的Ｌｅｗｉｓ酸催化剂，将这些催化剂进行缩醛、缩酮及酯化反应，有很好的催化活性，重复使用多次不失效．本文在合成此类催化剂的过程中利用热失重（ＴＧ）法及等离子光谱法（ＩＣＰ）等检测方法对合成此类催化剂的每一步进行跟踪检测，得到键合反应，开环反应及络合反应过程中的键合量，开环相量和ＴｉＣｌ＿４络合量的定量数据．对固载化催化剂表面的接枝量有所了解，从而可进一步检测此类催化剂的催化效应并得到一些启示．