The epoxidation of a series of α,β-unsaturated esters by dimethyldioxirane was studied. Second order rate constants were determined under pseudo first order conditions. The epoxide of each ester upon full conversion was found to be the only isolable product. Second order rate constants for the cis-like ethyl tiglate showed a 4 fold increase over that of trans-like angelic methyl ester. The ester substituent was found to have little effect on overall rate constants. A comparison of a relatively strained cyclopentene carboxylate to the cyclohexene carboxylate showed a 2 fold increase in selectivity for the former. Ethyl methacrylate displayed unexpected reactivity toward dioxirane; undergoing reaction faster than more substituted electron rich alkenes. Computer modeling studies using the AM-1 and density functional approaches were carried out to gain insights into the mechanistic aspects of the reaction. The esters in general favored the S-cis conformation or were evenly distributed among S-cis and S-trans except for the ethyl methacrylate case. The AM-1 approach did not predict the reactivity of open chain esters. The density functional approach predicted the relative reactivity of seven of the nine esters but could not predict the reactivity when the R1 group was substituted. One possible explanation is that the computer model predicts the methyl groups of the dioxirane to be positioned over the R1 group in the lowest energy of all other esters, but steric clash prevents this for angelic methyl ester and ethyl 3,3 dimethyl acrylate.

The reaction of dimethyldioxirane with a series of cis/trans-1,2-dialkylalkenes was carried out and produced the corresponding epoxides in high yield. As expected, the relative reactivity at 23 ºC of the cis-alkenes was at least 8-fold greater than that of the trans-counterparts with the magnitude of the relative reactivity increasing with increased steric bulk. Enhanced selectivity for cis- versus trans-alkene epoxidation was observed at lower temperatures. The reaction of dimethyldioxirane with selected alkenes was carried out in various solvent conditions (dried acetone:acetonitrile (1:9), dried acetone:methanol (1:9), dried acetone:carbon tetrachloride (1:9) and acetone:water (Xwater = 0.00, 0.01, 0.02, 0.03, 0.04, 0.05)) and produced the corresponding epoxides in high yield. The reactivity of dioxirane with simple di- and trialkylalkenes was enhanced as the polarity and hydrogen bonding capability of the solvent system were increased. Little to no change in reactivity was observed in the non-polar solvent system. Epoxidation of trisubstituted alkenes by dioxirane showed a greater rate enhancement in polar protic solvents compared to that for the epoxidation of the disubstituted alkenes. The epoxidation of an allylic alcohol by dimethyldioxirane showed a large increase in the non-polar solvent system compared to that in acetone. The reaction of dimethyldioxirane with the allylic alcohol also exhibited less of a rate increase in polar protic systems than its alkyl counterpart. Activation parameters for the epoxidation of cis/trans-1,2-dialkylalkenes by dioxirane in dried acetone and the previously mentioned solvent systems were determined using the Arrhenius method. In general, the ∆G‡ and ∆H‡ terms were greater for the reaction of dimethyldioxirane with trans-alkenes as compared to those for the corresponding cis-isomers regardless of solvent or alkyl steric bulk. The calculated ∆S‡ terms appeared essentially independent of steric bulk or solvent composition and were roughly identical, within experimental error, for all of the five cis/trans pairs. The ∆∆G‡ values, a comparison of the trans- to the cis-isomer data, yielded values of 1.2 to 1.8 kcal/mol in dried acetone for the five pairs of alkenes and appeared to be dependent on relative steric interactions. The ∆∆G‡ values for the epoxidation of cis/trans-alkenes carried out in solvents other than acetone showed no change from the value obtained in acetone. The experimental activation parameter data in dried acetone were consistent with predictions from ab initio calculations based on a spiro transition state model.

Nosso grupo de pesquisa vem se dedicado, há vários anos, ao estudo das reações de ciclização eletrofílica de substratos insaturados que contêm um nucleófilo interno (oxigênio ou nitrogênio). Este trabalho teve como objetivo obter derivados de éteres cíclicos de cinco e seis membros diferentemente funcionalizados. Compostos 1,3-dicarbonílicos e ß-hidróxi carbonílicos, contendo dupla ligação em posição apropriada, foram submetidos à reação de ciclização mediada tanto por iodo quanto por dimetildioxirana. De maneira semelhante, ß-enamino ésteres alquenilados foram submetidos à reação de iodociclização visando à síntese de diidropirróis, pirrolidínas e tetraidroindóis. Os heterociclos funcionalizados com iodo foram submetidos à reação de desidroiodação, promovida por base, fornecendo os correspondentes produtos de eliminação. / Our research group has been studying, for several years, eletrophilic cyclization reactions of unsaturated substrates bearing internal nucleophiles such as oxygen or nitrogen. This work aimed to obtain five and six membered cyclic ether derivatives differently functionalized. 1,3-Dicarbonyl and ß-hydroxy carbonyl compounds bearing double bonds suitably positioned were submitted to cyclization reaction mediated by either iodine or dimethyldioxirane. Similarly, alkenyl substituted ß-enamino esters were also prepared and submitted to iodo-cyclization reaction leading to dihydropyrrols, to pyrrolidines or to tetrahydroindols. The heterocyclic compounds bearing iodine were submitted to the corresponding dehydroiodination reaction mediated by base, furnishing elimination products

Nosso grupo de pesquisa vem se dedicado, há vários anos, ao estudo das reações de ciclização eletrofílica de substratos insaturados que contêm um nucleófilo interno (oxigênio ou nitrogênio). Este trabalho teve como objetivo obter derivados de éteres cíclicos de cinco e seis membros diferentemente funcionalizados. Compostos 1,3-dicarbonílicos e ß-hidróxi carbonílicos, contendo dupla ligação em posição apropriada, foram submetidos à reação de ciclização mediada tanto por iodo quanto por dimetildioxirana. De maneira semelhante, ß-enamino ésteres alquenilados foram submetidos à reação de iodociclização visando à síntese de diidropirróis, pirrolidínas e tetraidroindóis. Os heterociclos funcionalizados com iodo foram submetidos à reação de desidroiodação, promovida por base, fornecendo os correspondentes produtos de eliminação. / Our research group has been studying, for several years, eletrophilic cyclization reactions of unsaturated substrates bearing internal nucleophiles such as oxygen or nitrogen. This work aimed to obtain five and six membered cyclic ether derivatives differently functionalized. 1,3-Dicarbonyl and ß-hydroxy carbonyl compounds bearing double bonds suitably positioned were submitted to cyclization reaction mediated by either iodine or dimethyldioxirane. Similarly, alkenyl substituted ß-enamino esters were also prepared and submitted to iodo-cyclization reaction leading to dihydropyrrols, to pyrrolidines or to tetrahydroindols. The heterocyclic compounds bearing iodine were submitted to the corresponding dehydroiodination reaction mediated by base, furnishing elimination products

Kinetic studies determining the second order rate constants for the monoepoxidation of cyclic dienes, 1,3-cyclohexadiene and 1,3-cyclooctadiene, and the epoxidation of cis-/trans-2-hexenes by dimethyldioxirane (DMDO) were carried out using UV methodology. Consistent with published results, the kinetics of cis-/trans-2-hexenes by DMDO showed greater reactivity of the cis-isomer compared to that of the trans-compound. Molecular modeling studies for the epoxidation of a series of cis-/trans-alkenes, by DMDO were carried out using the DFT approach. The mechanism of epoxidation by DMDO was modeled by determining the transition state geometry and calculating the electronic activation energies and relative reactivities. The calculations were consistent with a concerted, electrophilic, exothermic process with a spiro-transition state for all cases. Kinetic studies for the monoepoxidation of the cyclic dienes showed a greater reactivity for 1,3-cyclohexadiene compared to that for 1,3-cyclooctadiene. The DFT method was employed to successfully model the transition state for the monoepoxidation of the cyclic dienes by DMDO and successfully predict the relative reactivities. Student misconceptions, at the high school and/or middle school level involving energy changes and chemical reactions have been prevalently noted in literature (by ACS and AAAS). Two examples of these misconceptions are: 1) heat is always needed to initiate a chemical reaction and 2) all chemical reactions create or destroy energy. In order to address these types of misconceptions, an educational module detailing the influence of energy changes on chemical reactions has been developed in conjunction with the Bio-bus program for middle and high school students. Visual aids and hands-on activities were developed in the module to potentially help students overcome/deal with the common misconceptions. Surveys were designed to access the situations (determine the extent of the misconceptions) and the effectiveness of the educational module, before and immediately after the module and one-month later to determine retention. The educational module has been presented to approximately 100 high school students from underrepresented communities. Pre-survey data confirmed the presence of the common misconceptions reported in the literature. Data from the post-survey indicated the new instructional module enhanced the student’s interest of science and expanded their content knowledge and laboratory skills. The post-survey data (immediately following the module) showed a significant difference in two out of five misconceptions when compared to the pre-survey data. However, this significance decreased when the 1-month post-survey data were compared to the pre-survey data.

Les symbioses bactérie-légumineuse (nodulation) et champignon-plante (mycorhization) présentent un intérêt agrobiologique et écologique majeur ; elles permettent aux plantes de croître naturellement sur un sol aride et peu fertile. Il a été démontré très récemment que les signaux impliqués dans la mise en place de la symbiose endomycorhizienne à arbuscule (facteurs "Myc") sont très proches de ceux de la nodulation. Il s'agit de molécules appartenant à la famille des lipo-chitooligosaccharides. Afin de réaliser la synthèse de ces molécules, deux nouvelles méthodologies ont été développées. L'ouverture oxydante d'acétals de 4,6-O-benzylidène de plusieurs glycopyranosides (en série gluco, galacto et manno) par le diméthyldioxirane (DMDO) a été étudiée. Le contrôle de la régiosélectivité a été effectué grâce au groupement protecteur introduit sur la fonction alcool de la position 3. La formation directe de β-glycosides de la N-acétyl-D-glucosamine par catalyse au triflate de fer (III) a été étudiée. La réaction a été menée sous irradiation micro-ondes ou en flux continu (système minifluidique Vapourtec®). Une nouvelle stratégie pour la synthèse du facteur [Myc-IV (C16:0, S)] a ensuite été établie. Nous avons utilisé un réactif peu toxique et non odorant pour introduire le motif thio nécessaire à la formation de deux liaisons glycosidiques. Le disaccharide précurseur de l'unité réductrice a été obtenu grâce à la première méthodologie développée au cours de cette thèse. / Arbuscular mycorrhiza (AM) is a root endosymbiosis between plants and fungi. It has an agrobiological interest and a crucial ecological importance because it allows plants to grow on aride and infertile soil. Recently, the structure of the symbiotic signal "Myc factor" was identified as a mixture of lipochitooligosaccharides (LCOs). In order to propose a new synthesis of LCOs, we developed two green methodologies in glycochemistry. We performed the oxidative cleavage of 4,6-O-benzylidene acetals of various glycopyranosides (gluco, manno and galacto series) with dimethyldioxirane (DMDO) and its regioselective control with a suitable protecting group at position 3. We investigated the formation of β-glycoside of N-acetyl-D-glucosamine using catalytic iron (III) triflate. The reaction can be performed using microwave irradiation or, for scale-up synthesis, flow chemistry using Vapourtec® minifluidic system. We establish a new strategy for the total synthesis of the most abundant Myc factor [Myc-IV (C16:0, S)]. We used odorless and few toxic MbpSH reagent to introduce the activated thio residue involved in two glycosylation reactions. The disaccharide acceptor precursor of the reducing end was obtained after oxidative cleavage of the 4,6-O-benzylidene moiety by DMDO.