Six-membered ring systems: with O and/or S atoms

A large variety of publications have emerged in 2012 involving O- and S-6- membered ring systems. The increasing number of reviews and other communica- tions dedicated to natural and synthetic derivatives and their biological significance highlights the importance of these heterocycles. Reviews on natural products involve biosynthesis and isolation of enantiomeric derivatives h12AGE4802i, biosynthesis, isolation, synthesis, and biological studies on the pederin family h12NPR980i and xanthones obtained from fungi, lichens, and bacteria h12CR3717i and on the potential chemotherapeutic value of phyto- chemical products and plant extracts as antidiabetic h12NPR580i, antimicrobial, and resistance-modifying agents h12NPR1007i. A more specific review covers a structure–activity relationship of endoperoxides from marine origin and their antitry- panosomal activity h12OBC7197i. New synthetic routes to naturally occurring, biologically active pyran derivatives have been the object of several papers. Different approaches have been discussed for the total synthesis of tetrahydropyran-containing natural products (")-zampanolide h12CEJ16868, 12EJO4130, 12OL3408i, (")-aspergillides A and B h12H(85)587, 12H(85)1255, 12TA252i, (þ)-neopeltolide h12JOC2225, 12JOC9840, 12H(85) 1255i, or their macrolactone core h12OBC3689, 12OL2346i. The total synthesis of bistramide A h12CEJ7452i and (þ)-kalihinol A h12CC901i and the stereoselec- tive synthesis of a fragment of bryostatin h12S3077, 12TL6163i have also been sur- veyed. Other papers relate the total synthesis of naturally occurring carbocyclic and heterocyclic-fused pyran compounds, such as (")-dysiherbaine h12CC6295i, penos- tatin B h12OL244i, Greek tobacco lactonic products, and analogues h12TL4293i and on the structurally intriguing limonoids andhraxylocarpins A–E h12CEJ14342i. The stereocontrolled synthesis of fused tetrahydropyrans was used in the preparation of blepharocalyxin D h12AGE3901i. Polyphenolic heterocyclic compounds have also received great attention in 2012. The biological activities and the chemistry of prenylated caged xanthones h12PCB78i, the occurrence of sesquiterpene coumarins h12PR77i, and the medicinal properties of the xanthone mangiferin h12MRME412i have been reviewed. An overview on the asymmetric syntheses of flavanones and chromanones h12EJO449i, on the synthesis and reactivity of flavones h12T8523i and xanthones h12COC2818i, on the synthesis and biosynthesis of biocoumarins h12T2553i, and on the synthesis and applications of flavylium compounds h12CSR869i has been discussed. The most recent developments in the synthesis and applications of sultones, a very important class of sulfur compounds, were reported h12CR5339i. A review on xanthene-based fluorescent probes for sensing cations, anions, bio- logical species, and enzyme activity has described the spiro-ring-opening approach with a focus on the major mechanisms controlling their luminescence behavior h12CR1910i. The design and synthesis of other derivatives to be used as sensors of gold species h12CC11229i and other specific metal cations h12PC823i have also been described. Recent advances related to coumarin-derived fluorescent chemosen- sors for metal ions h12COC2690i and to monitoring in vitro analysis and cellular imaging of monoamine oxidase activity h12CC6833i have been discussed. The study of various organic chromophores allowed the synthesis of novel dica- tionic phloroglucinol-type bisflavylium pigments h12SL2053i, and the optical and spectroscopic properties of several synthetic 6-aryldibenzo[b,d]pyrylium salts were explored h12TL6433i. Discussion of specific reactions leading to O- and S-membered heterocyclic compounds covers intramolecular radical cyclization h12S2475i and asymmetric enamine and dienamine catalysis h12EJO865i, oxa-Michael h12CSR988i and dom- ino Knoevenagel–hetero-Diels–Alder (hDA) reactions h12T5693i, and the versatility in cycloadditions as well as nucleophilic reactions using o-quinones h12CSR1050i. The use of specific reagents relevant to this chapter includes molecular iodine h12CEJ5460, 12COS561i, samarium diiodide–water for selective reductive transfor- mations h12CC330i, o-quinone methides as versatile intermediates h12CEJ9160i, InCl3 as catalyst h12T8683i, and gold and platinum p-acid mediated insertion of alkynes into carbon–heteroatom s-bonds h12S3401i. The remainder of this chapter discusses the most studied transformations on O- and S-6-membered heterocycles

친전자체에 의한 고리화반응을 이용한 디시허베인의 합성에 관한 연구

학위논문(석사) - 한국과학기술원 : 화학과, 2005.8, [ iv, 80 p. ]The furopyran core of dysiherbaine 1 was successfully synthesized via intramolecular epoxide opening in conjunction with electrophile-promoted cyclization. Our synthetic approach commenced in a palladium-catalyzed cross coupling under Stille conditions of cis-vinyl iodide 65 and tributyltin derivative 76 accessible from commercially-available starting materials, tris(hydroxymethyl)aminomethane $(TRIZMA^{\{cicledR})$ hydrochloride and D-mannitol, respectively. The resulting cis, cis diene intermediate 68 served as the precursor to epoxy alcohol 85. Protecting group modification of 68 followed by epoxidation afforded epoxy alcohol 85 which was designed to be the template for the ensuing cyclization reactions. The bicyclic framework was then assembled in sequence through a facile intramolecular epoxide opening of 85 to furnish tricyclic triol 88 bearing the requisite furan ring followed by mercurioetherification to undergo a six-membered ring cyclization thereby completing the furopyran ring to provide organomercurial product 96. Bicyclic diol 51 precursory to oxazolidinone 50, the chosen key intermediate to dysiherbaine was achieved upon reductive demercuration of 96. The key features in our synthetic strategy include the facile and efficient cyclization reactions and its convergence to provide the crucial intermediate prior to cyclization. Noteworthy also is the satisfactory yields in all key steps.한국과학기술원 : 화학과

Hemispheric Brain Dominance and Mathematics Performance of Western Visayas College of Science and Technology Students – Phase III

This study was anchored in the Split-Brain or Lateralization Theory of Roger Wolcott Sperry which states that the brain is divided into two hemispheres, the left hemisphere, and the right hemisphere. This was conducted to determine the significance of the difference in the mathematics(math) performance of the participants when they were grouped according to their hemispheric dominance (HD) and program. There were 172 first-year participants of Western Visayas College of Science and Technology, Iloilo City in phase I (SY 2011-2012). This was reduced to 120 participants in phase II (SY 2012-2013) and to 88 participants in phase III (SY 2013-2014). The participants’ HD was determined by the use of a researcher-made 46-item Hemispheric Brain Dominance Test while their mathematics performance was based on their average final grades in their Math classes. The statistical tools used were the mean, standard deviation, Mann-Whitney, Kruskal-Wallis, and Post hoc tests. The test in the hypothesis was set at .05 alpha level. Results showed that as an entire group, the left brain was the dominant brain hemisphere among the participants in phases I, II and III. In phase I and II, the participants had “fair” mathematics performance while phase III had “good” mathematics performance. When the participants were grouped according to their hemispheric dominance in phase I, the participants who were right-brain dominant had “conditional” mathematics performance while in phase II and III, they had “fair” mathematics performance. Those which were left-brain dominant in phase I had “fair” mathematics performance while in phase II and III, they had “good” mathematics performance. In phases, I, II and III of the study, significant differences existed in the level of mathematics performance when the participants were grouped according to their hemispheric brain dominance. The left brain dominant participants performed better in their mathematics performance than the right brain dominant participants. In phases, I, II and III, significant differences existed in the level of mathematics performance when the participants were grouped according to their program. The Post hoc (Scheffe) test results showed that BS Math significantly differs in their math performance from BSECE and BSMEAE participants. Furthermore, BSECE significantly differs in their math performance from BSEd and BSMEAE participants. Also, BSMEAE significantly differs from BSEE and BSEd participants in their math performance. There is no significant difference in the hemispheric brain dominance of the participants when they were grouped according to the phase of the study. This implies that the hemispheric brain dominance of the participants did not change for the last three years. It is highly recommended to administrators and guidance counselors to assess the brain dominance of the incoming freshmen and give priority to left-brained students for Math-laden courses. More researches should be conducted in different subjects, programs, and backgrounds to add support to this study.</jats:p

Hemispheric Brain Dominance and Mathematics Performance of Western Visayas College of Science and Technology Students – Phase IV

This is the last phase of a four-year study which aimed to determine the significance of the difference in the mathematics (math) performance of the participants when grouped according to their hemispheric dominance (HD). The study was anchored in the Split-Brain or Lateralization Theory of Roger Wolcott Sperry which states that the brain is divided into two hemispheres, the left, and the right hemisphere. The participants were eighty-eight (88) fourth-year college students from the courses of Bachelor of Science in Mathematics (BSM), Bachelor of Science in Education major in Mathematics (BSEd), Bachelor of Science in Electrical Engineering (BSEE), Bachelor of Science in Electronics and Communication Engineering (BSECE), and Bachelor of Science in Mechanical Engineering major in Automotive Engineering (BSMEAE) at Western Visayas College of Science and Technology SY 2014-2015. The participants’ HD was determined by the use of a researcher-made 46-item Hemispheric Brain Dominance Test while their mathematics performance was based on their Math classes average final grades. The statistical tools used were the mean, standard deviation, Mann-Whitney, Kruskal-Wallis, and Post hoc tests. The hypothesis was set at the 0.05 alpha level. As an entire group, the left brain was the dominant brain hemisphere among the participants from phase I to phase IV. When the participants were grouped according to program in phase I, the BSM, BSEd, and BSMEAE was left-brain dominant while the BSEE participants were right-brain dominant. The BSECE had an equal number of left-brained and right-brained participants. In phase II, the dominant brain hemisphere was the left brain. Only the BSEE participants were right-brain dominant. In phase III, the dominant brain hemisphere was the left brain, except for the BSMEAE where there was an equal number of left-brained and right-brained participants. In phase IV, all participants from the different programs were left-brained. Only the BSEE participants were right-brain dominant. As an entire group, phase I and II participants had “fair” mathematics performance; phase III had “good” mathematics performance, and phase IV had “very good” mathematics performance. When the participants who were right-brained were grouped according to mathematics performance, phase I had “conditional” mathematics performance; phase II and III had “fair” mathematics performance; and phase IV had “good” mathematics performance. Those who were left-brain dominant had “fair” mathematics performance in phase I, “good” mathematics performance in phase II and III, and “very good” mathematics performance in phase IV. In all phases of the study, significant differences existed in the level of mathematics performance when the participants were grouped according to their hemispheric brain dominance. The “left-brained” performed better in mathematics than the “right-brained”. There was a significant decrease in the enrolment of participants who were right-brain dominant because they shifted to other courses or they transferred to other schools. In phases, I, II and III, significant differences existed in the level of mathematics performance when the participants were grouped according to their program. There is no significant difference in the hemispheric brain dominance of the participants when grouped according to the phase of the study. This implies that the slight changes in the hemispheric brain dominance of the participants were not significant in the last four years.</jats:p