Synthesis of a 7-Membered Biaryl Guanidine Catalyst and its Use in the Vinylogous Aldol Reaction

The present thesis outlines the preparation of a 7-membered guanidine. Initial efforts to obtain this guanidine via 2-chloro-1,3-dimethylimidazolinium chloride induced ring forming chemistry failed to provide the target in a reproducible fashion. Changing strategies, we were able to obtain the desired guanidine through CuCl mediated amination of a 7-membered thiourea intermediate to arrive at the target. In addition, the catalytic activity of this compound was evaluated in a vinylogous aldol reaction of dibromofuranone and four aromatic aldehydes to generate chiral γ-butenolides with modest to good enantiomeric excess. It was found that electron-poor aldehydes resulted in higher, 81% ee, whereas electron rich aldehydes led to low, 41% ee, levels of enantiomeric excess.

Perceived learning needs in staff development of some care providers in five long-term care settings in Southern Ontario /

This exploratory descriptive study described what 20 care providers in 5 long-term care facilities perceived to aid or hinder their learning in a work-sponsored learning experience. A Critical Incident Technique (Woolsey, 1986) was the catalyst for the interviews with the culturally and professionally diverse participants. Through data analysis, as described by Moustakas (1994), I found that (a) humour, (b) the learning environment, (c) specific characteristics of the presenter such as moderate pacing, speaking slowly and with simple words, (d) decision-making authority, (e) relevance to practice, and (f) practical applications best met the study participants' learning needs. Conversely, other factors could hinder learning based on the participants' perceptions. These were: (a) other presenter characteristics such as a program that was delivered quickly or spoken at a level above the participants' comprehension, (b) no perceived relevance to practice, (c), other environmental situations, and (d) the timing of the learning session. One of my intentions was to identify the emic view among cultural groups and professional/vocational affiliations. A surprising finding of this study was that neither impacted noticeably on the perceived learning needs of the participants. Further research with a revised research design to facilitate inclusion of more diverse participants will aid in determining if the lack of a difference was unique to this sample or more generalizable on a case-to-case transfer basis to the study population.

Functional genomics of O-glucosyltransferases from Concord grape (Vitis labrusca)

Grape (Vitis spp.) is a culturally and economically important crop plant that has been cultivated for thousands of years, primarily for the production of wine. Grape berries accumulate a myriad of phenylpropanoid secondary metabolites, many of which are glucosylated in plantae More than 90 O-glucosyltransferases have been cloned and biochemically characterized from plants, only two of which have been isolated from Vitis spp. The world-wide economic importance of grapes as a crop plant, the human health benefits associated with increased consumption of grape-derived metabolites, the biological relevance of glucosylation, and the lack of information about Vitis glucosyltransferases has inspired the identification, cloning and biochemical characterization of five novel "family 1" O-glucosyltransferases from Concord grape (Vitis labrusca cv. Concord). Protein purification and associated protein sequencIng led to the molecular cloning of UDP-glucose: resveratrollhydroxycinnamic acid O-glucosyltransferase (VLRSGT) from Vitis labrusca berry mesocarp tissue. In addition to being the first glucosyltransferase which accepts trans-resveratrol as a substrate to be characterized in vitro, the recombinant VLRSGT preferentially produces the glucose esters of hydroxycinnamic acids at pH 6.0, and the glucosides of trans-resveratrol and flavonols at 'pH 9.0; the first demonstration of pH-dependent bifunctional glucosylation for this class of enzymes. Gene expression and metabolite profiling support a role for this enzyme in the bifuncitonal glucosylation ofstilbenes and hydroxycinnamic acids in plantae A homology-based approach to cloning was used to identify three enzymes from the Vitis vinifera TIGR grape gene index which had high levels of protein sequence iii identity to previously characterized UDP-glucose: anthocyanin 5-0-glucosyltransferases. Molecular cloning and biochemical characterization demonstrated that these enzymes (rVLOGTl, rVLOGT2, rVLOGT3) glucosylate the 7-0-position of flavonols and the xenobiotic 2,4,5-trichlorophenol (TCP), but not anthocyanins. Variable gene expression throughout grape berry development and enzyme assays with native grape berry protein are consistent with a role for these enzymes in the glucosylation of flavonols; while the broad substrate specificity, the ability of these enzymes to glucosylate TCP and expression of these genes in tissues which are subject to pathogen attack (berry, flower, bud) is consistent with a role for these genes in the plant defense response. Additionally, the Vitis labrusca UDP-glucose: flavonoid 3-0-glucosyltransferase (VL3GT) was identified, cloned and characterized. VL3GT has 96 % protein sequence identity to the previously characterized Vitis vinifera flavonoid 3-0-glucosyltransferase (VV3GT); and glucosylates the 3-0-position of anthocyanidins and flavonols in vitro. Despite high levels of protein sequence identity, VL3GT has distinct biochemical characteristics (as compared to VV3GT), including a preference for B-ring methylated flavonoids and the inability to use UDP-galactose as a donor substrate. RT-PCR analysis of VL3GT gene expression and enzyme assays with native grape protein is consistent with an in planta role for this enzyme in the glucosylation of anthocyanidins,but not flavonols. These studies reveal the power of combining several biochemistry- and molecular biology-based tools to identify, clone, biochemically characterize and elucidate the in planta function of several biologically relevant O-glucosyltransferases from Vitis spp.

Exploring the personal and professional lives of teachers in the search for authenticity /

"We teach who we are" (Palmer, 1998, p. 2). This simple, yet profound, statement was the catalyst that began my thesis journey. Using a combination of self-study and participant narratives, Palmer's idea was explored as search for authenticity. The self-study component of this narrative was enhanced by the stories of two other teachers, both women. I chose to use narrative methodology to uncover and discover the relationship between the personal and professional lives of being a teacher. Do teachers express themselves daily in their classrooms? Do any lessons from the classroom translate into teachers' personal lives? The themes of reflection, authenticity, truth, and professional development thread themselves throughout this narrative study. In order to be true to myself as a teacher/researcher, arts-based interpretations accompany my own and each participant's profile. Our conversations about our pasts, our growth as teachers and journeys as individuals were captured in poetry and photographic mosaics. Through rich and detailed stories we explored who we are as teachers and how we became this way. The symbiotic relationship between our personal and professional lives was illustrated by tales of bravery, self-discovery, and reflection. The revelations uncovered illustrate the powerful role our past plays in shaping the present and potentially the friture. It may seem indulgent to spend time exploring who we are as teachers in a time that is increasingly focused on improving student test scores. Yet, the truth remains that, "Knowing myself is as crucial to good teaching as knowing my students and my subject" (Palmer, 1998, p. 2).

Kinetic studies of the effect of organic sulphides on the oxidation of other sulphides /

The rates of oxidation of three Organic sulphides viz. methyl phenyl sulphide, (P), p -me thoxyphenyl methyl sulphide (M) and methyl p-nitrophenyl sulphide (N). have been obtained in ethanol using MoO-(acac)- as catalyst and Bu OOH as the oxidizing agent. A Hammett plot gave a rho value of -2.1 and the activation energies for the oxidation of P, M and N were estimated to be 63.60, 40.12 and 197.46 Kj mol respectively. The effect of organic sulphide on the oxidation of another sulphide was also ascertained. Positive and negative deviations were observed from the expected slope.

The Catharanthus roseus 16-hydroxytabersonine O-methyltransferase involved in vindoline biosynthesis /

Madagascar periwinkle (Catharanthus roseus) produces the well known and remarkably complex dimeric anticancer alkaloids vinblastine and vincristine that are derived by coupling vindoline and catharanthine monomers. This thesis describes the novel application of carborundum abrasion (CA) technique as a tool for large scale isolation of leaf epidermis enriched proteins. This technique was used to facilitate the purification to apparent homogeneity of 16-hydroxytabersonine-16-0-methyltransferse (l60MT) that catalyses the second step in the 6 step pathway that converts tabersonine into vindoline. This versatile tool was also used to harvest leaf epidermis enriched mRNAs that facilitated the molecular cloning of the 160MT. Functional expression and biochemical characterization of recombinant 160MT enzyme showed that it had a very narrow substrate specificity and high affinity for 16-hydroxytabersonine, since other closely related monoterpene indole alkaloids (MIAs) did not act as substrates. In addition to allowing the cloning of this gene, CA technique clearly showed that 160MT is predominantly expressed in Catharanthus leaf epidermis, in contrast to several other OMTs that appear to be expressed in other Catharanthus tissues. The results provide compelling evidence that most of the pathway for vindoline biosynthesis including the 0- methylation of 16-hydroxytabersonine occurs exclusively in leaf epidermis, with subsequent steps occurring in other leaf cell types. Small molecule O-methyltransferases (OMTs) (E.C. 2.1.1.6.x) catalyze the transfer of the reactive methyl group of S-adenosyl-L-methionine (SAM) to free hydroxyl groups of acceptor molecules. Plant OMTs, unlike their monomeric mammalian homologues, exist as functional homodimers. While the biological advantages for dimer fonnation with plant OMTs remain to be established, studies with OMTs from the benzylisoquinoline producing plant, Thalictrum tuberosum, showed that co-expression of 2 recombinant OMTs produced novel substrate specificities not found when each rOMT was expressed individually (Frick, Kutchan, 1999) . These results suggest that OMTs can fonn heterodimers that confer novel substrate specificities not possible with the homodimer alone. The present study describes a 160MT model based strategy attempting to modify the substrate specificity by site-specific mutagenesis. Our failure to generate altered substrate acceptance profiles in our 160MT mutants has lead us to study the biochemical properties ofhomodimers and heterodimers. Experimental evidence is provided to show that active sites found on OMT dimers function independently and that bifunctional heterodimeric OMTs may be fonned in vivo to produce a broader and more diverse range of natural products in plants.

A narrative journey of teacher reflexivity and authenticity in technological environments /

This qualitative narrative inquiry was driven by my desire to further explore my personal discovery that my utilization of educational technologies in teaching and learning environments seemed to heighten a sense of creativity, which in turn increased reflective practice and authenticity in my teaching. A narrative inquiry approach was used as it offered the opportunity to uncover the deeper meanings of authenticity and reflection as participants' personal experiences were coconstructed and reconstructed in relationship with me and in relationship to a social milieu. To gain further insight into this potential phenomenon, I engaged in 2 conversational interviews with 2 other teachers from an Ontario College in a large urban centre who have utilized educational technologies in their teaching and learning communities and I maintained a research journal, constructed during the interview process, to record my own emerging narrative accounts, reflections, insights and further questions. The field texts consisted of transcriptions of the interviews and my reflective journal. Research texts were developed as field texts were listened to multiple times and texts were examined for meanings and themes. The educational technologies that both women focused on in the interview were digital video of children as they play, learn and develop and the use of an audible teacher voice in online courses. The invitation given to students to explore and discover meaning in videos of children as they watched them with the teacher seemed to be a catalyst for authenticity and a sense of synergy in the classroom. The power of the audible teacher voice came through as an essential component in online learning environments to offer students a sense of humanness and connection with the teacher. Relationships in both online and face to face classrooms emerged as a necessary and central component to all teaching and learning communities. The theme of paradox also emerged as participants recognized that educational technologies can be used in ways that enhance creativity, authenticity, reflection and relationships or in ways that hinder these qualities in the teaching and learning community. Knowledge of the common experiences of college educators who utilize educational technologies, specifically digital video of children to educate early childhood educators, might give meaning and insight to inform the practice of other teachers who seek authentic, reflexive practice in the classroom and in on line environments.

Aspects of the hemes and modulation of hydrogen donors in catalases from bovine liver, yeast, and escherichia coli

Catalase is the enzyme which decomposes hydrogen peroxide to water and oxygen. Escherichia coli contains two catalases. Hydroperoxidase I (HPI) is a bifunctional catalase-peroxidase. Hydroperoxidase II (HPII) is only catalytically active toward H202. Expression of the genes encoding these proteins is controlled by different regimes. HPJI is thought to be a hexamer, having one heme d cis group per enzymatic subunit. HPII wild type protein and heme containing mutant proteins were obtained from the laboratory of P. Loewen (Univ. of Manitoba). Mutants constructed by oligonucleotidedirected mutagenesis were targeted for replacement of either the His128 residue or the Asn201 residue in the vicinity of the HPII heme crevice. His128 is the residue thought to be analogous to the His74 distal axial ligand of the heme in the bovine liver enzyme, and Asn201 is believed to be a residue critical to the function of the enzyme because of its role in orienting and interacting with the substrate molecule. Investigation of the nature of the hemes via absorption spectroscopy of the unmodified catalase proteins and their derived pyridine hemochromes showed that while the bovine and Saccharomyces cerevisiae catalase enzymes are protoheme-containing, the HPII wild type protein contains heme d, and the mutant proteins contain either solely protoheme, or heme d-protoheme mixtures. Cyanide binding studies supported this, as ligand binding was monophasic for the bovine, Saccharomyces cerevisiae, and wild type HPII enzymes, but biphasic for several of the HPII mutant proteins. Several mammalian catalases, and at least two prokaryotic catalases, are known to be NADPH binding. The function of this cofactor appears to be the prevention of inactivation of the enzyme, which occurs via formation of the inactive secondary catalase peroxide compound (compound II). No physiologically plausible scheme has yet been proposed for the NADPH mediation of catalase activity. This study has shown, via fluorescence and affinity chromatography techniques, that NADPH binds to the T (Typical) and A (Atypical) catalases of Saccharomyces cerevisiae, and that wild type HPII apparently does not bind NADPH. This study has also shown that NADPH is unlike any other hydrogen donor to catalase, and addresses its features as a unique donor by proposing a mechanism whereby NADPH is oxidized and catalase is protected from inactivation via the formation of protein radical species. Migration of this radical to a position close to the NADPH is also proposed as an adjunct hypothesis, based on similar electron migrations that are known to occur within metmyoglobin and cytochrome c peroxidase when reacted with H202. Validation of these hypotheses may be obtained in appropriate future experiments.

Intramolecular carbenoid insertion : reactions of [alpha] -diazoketones derived from benzothienyl, pyrolyl and indolyl alkanoic acids with rhodium (II) acetate

Recent studies have shown that the rhodium (II) acetate decomposition chemistry observed for a-diazoketones tethered to thienyl, furanyl, and benzofuranyl moieties is dependent not only on the nature of the heteroatom but also on the length of the aliphatic tether linking the diazoketone moiety with the aromatic fragment. The present thesis expands on these results and focuses on a-diazoketones tethered to benzothiophenes, pyrroles and indoles by a methylene linker. In the case of benzothiophenes, it was shown that the rhodium catalyst decomposition of I-diazo-4-(3-benzothienyl)-2-butanone (146) and 1-diazo-4-(3benzothienyl)- 2-butanone (152) allow for the isolation of 1,2,3a,3b-tetrahydro-3Hbenzo[ b]cyclopenta[1,3]cyclopropa- [1 ,2-d]thiophen-3-one (147) and 1,2,3a,3btetrahydro- 3H-benzo[b]cyclopenta[1,3]cyclopropa[1,2-d]thiophen-3-one (153). However treatment of 1-diazo-3-(3-Benzothienyl)-2-Propanone (165) with Rh(II) acetate results in the formation of 2,3-Dihydro-1H-benzo[b]cyclopenta[d]thiophen-2-one (159), while 1diazo- 3-(2-Benzothienyl)-2-Propanone with the same condition gives 5,5-bis( 1benzothiophen- 2-ylmethyl)-2(5H)-furanone (166) along with the tricycle 159. The chemistry of the pyrrolyl and the indolyl moieties linked to terminal adiazoketone systems was also investigated. The decomposition of I-diazo-(2-pyrrolyl)-2propanone (173) results in the formation of two products; the N-H insertion product IHpyrrolizin- 2(3H)-one (176) and the alkylation product 4,6-dihydrocyclopenta[b]pyrrol5( 1 H)-one (180). When 1-Diazo-3-(3-indoly)-3-propanone (194) is treated with catalytic amount of Rh (II) 3,4-dihydrocyclopenta[b]indol-2(1H)-one (193) is isolated quantitatively. The later reaction when monitored using IH NMR the intermediate 200 can be seen whose structure was confirmed by the comparison to series of model compounds. The mechanisms underlying these reactions as well as their synthetic utility is discussed.

Kinetic and mechanistic studies for the molybdenum- catalyzed oxidation of organic sulfides and olefins by t- DuO2H

This research was focussed on the effects of light, solvent and substituents in the molybdenum-catalyzed oxidation of phenylmethyl sulfides with t-Bu02H and on the effect of light in the molybdenum-catalyzed epoxidation of l-octene with t-Bu02H. It was shown that the Mo(CO)6-catalyzed oxidation of phenylmethyl sulfide with t-Bu02H~ at 35°C, proceeds 278 times faster underUV light than under laboratory lighting, whereas the Mo02(acac)2-catalyzed oxidation proceeds only 1.7 times faster under UV light than under normal laboratory lighting. The difference between the activities of both catalysts was explained by the formation of the catalytically active species, Mo(VI). The formation of the Mo(VI) species, from Mo(CO)6 was observed from the IR spectrum of Mo(CO)6 in the carbonyl region. The Mo(CO)6-catalyzed epoxidation of l-octene with t-Bu02H showed that the reaction proceeded 4.6 times faster under UV light than in the dark or under normal laboratory lighting; the rates of epoxidations were found to be the same in the dark and under normal laboratory lighting. The kinetics of the epoxidations of l-octene with t-Bu02H, catalyzed by Mo02(acac)2 were found to be complicated; after fast initial rates, the epoxidation rates decreased with time. The effect of phenylmethyl sulfide on the Mo(CO)6-catalyzed epoxidation of l-octene waS studied. It was shown that instead of phenylmethyl sulfide, phenylmethyl sulfone, which formed rapidly at 85°C, lowered the reaction rate. The epoxidation of l-octene was found to be 2.5 times faster in benzene than in ethanol. The substituent effect on the Mo02(acac)2-catalyzed oxidations of p-OH, p-CHgO, P-CH3' p-H, p-Cl, p-Br, p-CHgCO, p-HCO and P-N02 substituted phenylmethyl sulfides were studied. The oxidations followed second order kinetics for each case; first order dependency on catalyst concentration was also observed in the oxidation of p-CHgOPhSMeand PhSMe. It was found that electron-donating groups on the para position of phenylmethyl sulfide increased the rate of reaction, while electronwithdrawing groups caused the reaction rate to decrease. The reaction constants 0 were determined by using 0, 0- and 0* constants. The rate effects were paralleled by the activation energies for oxidation. The decomposition of t-Bu02H in the presence of M.o (CO)6, Mo02 (acac)2 and VO(acac)2 was studied. The rates of decomposition were found to be very small compared to the oxidation rates at high concentration of catalysis. The relative rates of the Mo02(acac)2-catalyzed oxidation of p-N02PhSMe by t-Bu02H in the presence of either p-CH30PhSMe or PhSMe clearly show that PhSMe and p-CHgOPhSMe act as co-catalysts in the oxidation of p-N02PhSMe. Benzene, mesity1ene and cyclohexane were used to determine the effect of solvent in the Mo02 (acac)2 and Mo(CO)6-catalyzed oxidation of phenylmethyl sulfide. The results showed that in the absence of hydroxylic solvent, a second molecule of t-Bu02H was involved in the transition state. The complexation of the solvent with the catalyst could not be explained.The oxidations of diphenyl sulfoxide catalyzed by VO(acac)2, Mo(CO)6 and Mo02(acac)2 showed that VO(acac)2 catalyzed the oxidation faster than Mo(CO)6 and Mo02 (acac)2_ Moreover, the Mo(CO)6-catalyzed oxidation of diphenyl sulfoxide proceeded under UV light at 35°C.

Miniature Wulff-type generator for improving feed to fuel cells /|nT.-S. Tan. -- 260 St. Catharines, Ont. : [s. n.],

The original objective of this work was to provide a simple generator w.hich would produce hydrogen torLfuel-cell feed and which could be operated under remote or northern conditions. A secondary objective was to maximize the yield of hydrogen and carbon monoxide from available feed-stocks. A search of the patent literature has indicated that the concept of a small Wulff-type generator is essentially sound and that hydrogen may be recovered from a wide variety of hydrocarbon feed-stocks. A simple experimental set-up has been devised, patterned after ~~t originally used by R. G. Wulff for producing acetylene. This provides a supply of feed-stock, with or Without a carrier gas, which may be passed directly through a heated tube, which may contain a catalyst. A suitable procedure has been devised for analysi~ effluent gases for hydrogen, oxygen, nitrogen, methane and carbon monoxide by gas chromatography with the column packed with .Molecular .:>ieve .5 4. Athanol with air a.s carrier gas and at the same time as oxidant o was thermolyzed at temperatures in the ra~e 700-1100 C, with or Wi~lout catalyst. Methanol with or without nitrogen as a carrier gas was also cracked with • the same type of reactor refractory tube, but the temperature range was lower t down to ,300 " C when a catalyst was used. The problems of converting methane to hydrogen and carbon monoxide effiCiently, using air and/or water as oxidants were also studied.

Phospha-adamantanes as ligands for palladium-catalyzed cross-coupling reactions

New and robust methodologies have been designed for palladium-catalyzed crosscoupling reactions involving·a novel·class oftertiary phosphine ligand incorporating a phospha-adamantane framework. It has been realized that bulky, electron-rich phosphines, when used as ligands for palladium, allow for cross-coupling reactions involving even the less reactive aryl halide substrates with a variety of coupling partners. In an effort to design new ligands suitable for carrying out cross-coupling transformations, the secondary phosphine, 1,3,5,7-tetramethyl-2,4,8-trioxa-6phosphaadamantane was converted into a number of tertiary phosphine derivatives. The ability of these tertiary phosphaadamantanes to act as effective ligands in the palladiumcatalyzed Suzuki cross-coupling was examined. 1,3,5,7-Tetramethyl-6-phenyl-2,4,8trioxa- 6-phosphaadamantane (PA-Ph) used in combination with Pdz(dba)3permitted the reaction of an array of aryl iodides, bromides and chlorides with a variety arylboronic acids to give biaryls in good to excellent yields. Subsequently, palladium complexes of PA-Ph were prepared and isolated in high yields as air stable palladium bisphosphine complexes. Two different kinds of crystals were isolated and upon characterization revealed two complexes, Pd(PA-Ph)z.dba and Pd(PA-Ph)zOz. Preliminary screening for their catalytic activity indicated that the former is more reactive than the latter. Pd(PAPh) z.dba was applied as the catalyst for Sonogashira cross-coupling reactions of aryl iodides and bromides and in the reactions of aryl bromides and chlorides with ketones to give a-arylated ketones at mild temperatures in high yields.

Sol-gel routes to supported Friedel-Crafts alkylation catalysts

Aluminosilicate catalysts containing supported ZnCl2 and metal fluoride salts have been prepared using a sol-gel based route, tested and characterized. The activities of these ZnCl2 + metal fluoride catalysts, while greater than "Clayzic" (ZnCI2 supported on montmorillonite KIO) are not as good as supported ZnCl2 only supported on aluminosilicate. Alumina supports have also been prepared via a sol-gel route using various chemical additives to generate a mesoporous structure, loaded with ZnCl2 and tested for activity. The activities for these alumina-supported catalysts are also significantly higher than that of "Clayzic", an effective Friedel-Crafts catalyst. Characterizations of these two types of catalysts were done by magic angle spinning (MAS) NMR, diffuse reflectance infrared (DRIFT) spectroscopy and additionally for the alumina nitrogen adsorption studies were done. Supported aluminum trichloride was also investigated as an alternative to the traditional use of aluminum trichloride.

The importance of hydrogen bonding in the alkylation of phenols

Hydrogen bond assisted alkylation of phenols is compared with the classical base assisted reactions. The influence of solvents on the fluoride assisted reactions is discussed,· with emphasis on the localization of hydrogen bond charge density. Polar aprotic solvents such as DMF favour a-alkylation, and nonpolar aprotic solvents such as toluene favourC-alkylation of phenol. For more reactive and soluble fluorides, such as tetrabu~ylammoniumfluoride, the polar aprotic solvent favours a-alkylation and nonpolar aprotic solvent favours fluorination. Freeze-dried potassium fluoride is a better catalytic agent in hydrogen bond assisted alkylation reactions of phenol than the oven-dried fluoride. The presence of water in the alkylation reactions reduces the expected yield drastically. The tolerance of the reaction to water has also been studied. The use ofa phase transfer catalyst such as tetrabutylammonium bromide in the alkylation reactions of phenol in the presence of potassium fluoride is very effective under anhydrous conditions. Sterically hindered phenols such as 2,6-ditertiarybutyl-4-methyl phenol could not be alkylated even by using the more reactive fluorides, such as tetrabutylammonium fluoride in either polar or nonpolar aprotic solvents. Attempts were also made to alkylate phenols in the presence of triphenylphosphine oxide.

The versatility and utilization of phosphorus based compounds in classic carbon-carbon bond forming and esterification reactions

The phosphonium salt room temperature ionic liquid tetradecyltrihexylphosphonium chloride (THPC) has been employed as an efficient reusable media for the palladium catalyzed Suzuki cross-coupling reaction of aryl halides, including aryl chlorides, under mild conditions. The cross-coupling reactions were found to proceed in THPC containing small amounts ofwater and toluene (single phase) using potassium phosphate and 1% Pd2(dba)3'CHCI3. Variously substituted iodobenzenes, including electron rich derivatives, reacted efficiently in THPC with a variety of arylboronic acids and were all complete within 1 hour at 50°C. The corresponding aryl bromides also reacted under these conditions with the addition of a catalytic amount of triphenylphosphine that allowed for complete conversion and high isolated yields. The reactions involving aryl chlorides were considerably slower, although the addition of triphenylphosphine and heating at 70°C allowed high conversion of electron deficient derivatives. Addition of water and hexane to the reaction products results in a triphasic system, from which the catalyst was then recycled by removing the top (hexanes) and bottom (aqueous) layers and adding the reagents to the ionic liquid which was heated again at 50°C; resulting in complete turnover of iodobenzene. Repetition of this procedure gave the biphenyl product in 82-97% yield (repeated five times) for both the initial and recycled reaction sequences. IL ESTERIFICATIONREACTION A new class oftrialkylphosphorane has been prepared through reaction of a trialkylphosphine with 2-chlorodimethylmalonate in the presence oftriethylamine. These new reagents promote the condensation reaction of carboxylic acids with alcohols to provide esters along with trialkylphosphine oxide and dimethylmalonate. The condensation reaction of chiral secondary alcohols can be controlled to give either high levels of inversion or retention through a subtle interplay involving basicity of the reaction media, solvent, and tuning the electronic and steric nature of the carboxylic acid and stenc nature of the phosphorane employed. A coherent mechanism is postulated to explain these observations involving reaction via an initial acyloxyphosphonium ion.