Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
Results
Showing 1 to 20 of 38 for “"[4 + 2] cycloaddition"”.
-
Synthesis of nitrogen heterocycles via the intramolecular [4+2] cycloaddition of iminoacetonitriles
… anomeric effect. The substrates for these [4+2] cycloadditions are prepared from readily available alcohols via a Mitsunobu reaction with the previously unknown N-cyanomethyltriflamide (HN(Tf)CH₂CN) followed by cesium carbonate promoted elimination of trifluoromethanesulfinate. The a-amino …
-
Mechanistic and synthetic studies of the intramolecular [4+2] cycloaddition of conjugated enynes
… mechanism and scope of the intramolecular [4+2] cycloaddition of conjugated enynes has shown the reaction likely proceeds by a concerted cycloaddition of the enyne to give a highly reactive cyclic allene intermediate which isomerizes to aromatic and dihydroaromatic compounds through proton …
-
Operation Hot Sandwich: Incorporating pyrones in [4 + 2] cycloaddition reactions to prepare thermorubin
… After attempts to use single sulfoxide cycloaddition products failed to propagate, a new donor substrate needed to be created: a symmetrical intermediate already containing both phenyl sulfoxide functionalities. This material was tested and proved successful with further optimization …
-
Synthesis of polycyclic heteroaromatic compounds via the intramolecular [4+2] cycloaddition of conjugated hetarenynes and alkynes
… feasibility and scope of intramolecular [4+2] cycloadditions of hetarenynes and alkynes as a method for the synthesis of polycyclic benzo[b]-fused five-membered heteroaromatic compounds. Only scattered reports of this transformation existed prior to our work and these were very limited in their …
-
Applications of nitroalkene (4+2); cycloaddition chemistry. The asymmetric synthesis of substituted pyrrolidines and the total synthesis of mesembrine
… were found to undergo Lewis acid-promoted (4+2) cycloadditions with n-butyl vinyl ether to afford cyclic nitronates in 76-90% yield. The resulting nitronates were reduced with hydrogen in the presence of platinum oxide to afford 3,3-disubstituted pyrrolidines which were isolated in 70-83% yield …
-
Studies on the stereo- and regiochemistry of [4+2] cycloaddition of nitroso compounds to chiral halobenzenediols. Total synthesis of lycoricidine
… to study the regio- and stereochemistry of the cycloaddition. The addition of dienophiles to the acetonide of the diols was anti in every case. When ethyl propiolate was used, two regioisomers 7 and 8 were obtained. In contrast, the addition of nitroso dienophiles, derived in situ from the …
-
Inter- and intramolecular (4+2) cycloaddition reactions and tandem inter- and intramolecular (4+2)/intramolecular (3+2)cycloaddition reactions of nitroalkenes
Both inter- and intramolecular cycloadditions of nitroalkenes with Lewis acid catalysis were investigated. The intramolecular cycloadditions of nitroalkenes were found to be completely stereoselective for trisubstituted nitroalkenes. Intermolecular cycloadditions of aromatic nitroalkenes were found …
-
Synthesis of indolines and indoles via intramolecular [4 + 2] cycloaddition of ynamides and conjugated enynes ; Synthesis of nitrogen heterocycles in supercritical carbon dioxide
… with conjugated enynes in intramolecular [4 + 2] cycloaddition to afford substituted indolines that undergo oxidation with o-chloranil to furnish the corresponding indoles. The cycloaddition substrates are easily assembled from derivatives of 3-butynylamine by Sonogashira coupling with alkenyl …
-
TRANSITION METAL MEDIATED, STEREOSELECTIVE HIGHER-ORDER [6+4] AND DIELS-ALDER [4+2] CYCLOADDITION REACTIONS: SYNTHESIS OF NOVEL 2-SILYL SUBSTITUTED-1,3-DIENYL COMPOUNDS AND THEIR DOMINO REACTIONS
We have prepared various substituted cobaloxime dienes and studied extensively their reactivities in Diels-Alder reactions. Based on the studies with cobaloxime chemistry, we concluded that increased exo selectivities were possible with the insertion of the transition metals in the 2-position of …
-
Tandem Cycloaddition Chemistry: Part I. Synthesis and Crystallographic Analysis of 1-Azafenestranes. Part II. Synthesis and Reactivity of N-Vinyl Nitrones
Tandem cycloaddition chemistry has been explored with regard to the synthesis and crystallographic analysis of molecules of theoretical interest, the 1-azafenestranes, and the development of a new type of heterodiene, the N-vinyl nitrone. The tandem [4+2]/[3+2] cycloaddition of a nitrocyclopentene …
-
Triplex Diels-Alder reactions of beta-methylstyrenes. Density functional investigation of pion-pion interactions
The (4+2) cycloaddition of an electron-rich diene to an electron-rich dienophile may be catalyzed by irradiation of a cyanoarene. This reaction is shown to proceed through an intermediate ternary excited state complex (triplex) and is therefore called the triplex Diels-Alder reaction. Evidence is …
-
Studies directed toward the total synthesis of salvilenone
… precursors followed by an intramolecular [4 + 2] cycloaddition of a conjugated enyne and benzyne intermediate.
-
The total syntheses of (+)-crotanecine, (-)-hastanecine and (-)-rosmarinecine utilizing the tandem (4+2)/(3+2) cycloadditions of nitroalkenes
… is a sequential inter (4+2) /inter (3+2) cycloaddition. The Lewis acid promoted (4+2) cycloaddition between 2-acyloxy nitroalkene 90 and chiral vinyl ether (+)-28 afforded a nitronate which underwent facile (3+2) cycloaddition with dimethyl maleate. The resulting nitroso acetal (${-}$)-96 …
-
[4 + 2] cycloadditions of iminoacetonitriles : synthesis of highly substituted tetrahydropyridines and indolizidine alkaloids
… the scope of the intermolecular [4 + 2] cycloaddition of N-benzyliminoacetonitrile with unactivated and activated dienes, as well as, the synthetic elaboration of the cycloadducts. This thesis also describes the worked performed to complete the total syntheses of indolizidines (-)- 235B', …
-
Stereochemical Course of the Tandem [4+2]/[3+2] Cycloaddition of Nitroalkenes
The [4+2] cycloaddition of nitrobutene was further examined with both experimental and theoretical studies. Small, soft Lewis acids (such as Me 3Al) promote endo cycloaddition with the vinyl ether reacting in an s-trans conformation. Most other Lewis acids favor exo cycloaddition due either to …
-
Chemoselective and Stereoselective Exploration of the Chemical Reactivity Space of Castagnoli-Cushman-Derived Allylic Lactamoyl Esters: Application to the Synthesis of Aza-Polycyclic Architectures
… outcomes are achieved through a novel [4 + 2] cycloaddition reaction between an <em>N</em>-iodoarylated-1,3-azadiene and cyclic anhydrides, followed by interception of the cycloadducts in cross-coupling manifolds (<em>e.g.</em>, Sonogashira coupling) and concomitant lithiation-cyclization of …
-
The synthesis and use of cyclic nitronic esters
The Lewis acid promoted (4+2) cycloaddition of nitrostyrenes with various dienophiles was examined and several issues of selectivity were addressed. Anti diastereomers are formed exclusively in high yields in the cycloaddition with cyclic alkenes. Lewis acid complexation was examined by conducting …
-
Biomimetic synthesis of natural products via reactions of ortho-quinone methides
… enol ether was employed for the biomimetic [4+2] cycloaddition reaction to afford a simplified virgatolide B analogue. An isomerised compound containing a cis fused ring junction, thought to arise via a [4+2] cycloaddition of an ortho-quinone methide and an endocyclic enol ether formed by acid …
-
Development of Nickel and Zirconium Mediated Cycloadditions for the Synthesis of Substituted Pentacene
The regioselectivity of the [2+2+2] cycloaddition of nickel-benzynes and 1,3-diynes could be maintained when asymmetrically substituted 1,3-diynes were employed. The ability to incorporate an asymmetric 1,3-diyne into the oligoacene backbone provided substituents that could be differentiated in …
-
Gold-catalyzed synthesis and functionalization of heteroarenes
… The second chapter is focused on the cycloaddition reaction of 2-vinylindoles with enones towards the preparation of tetrahydrocarbazole derivatives. This process has been studies using classic Lewis acids and gold complexes as catalysts. According to the results, gold catalysts proved …
Page 1 of 2