Search results for "Cycloaddition"
showing 10 items of 392 documents
The role of the trifluoromethyl group in reactivity and selectivity in polar cycloaddition reactions. A DFT study
2012
Abstract The role of the trifluoromethyl group in reactivity, regio-, and stereoselectivity in cycloaddition reactions has been analyzed by studying the 1,3-dipolar cycloaddition (13DC) reactions of nitrone 4 with 3,3,3-trifluoro-1-nitropropene 7b and 3,3,3-trifluoro-2-nitropropene 14 using density functional theory (DFT) methods at the B3LYP/6-311G(d) level. The recent M06-2X functional has also been evaluated but, although the thermodynamic performance is improved, the kinetic data are not necessarily better than those obtained by the popular B3LYP functional for cycloaddition reactions. Four reactive channels associated with the meta and ortho regio- and endo and exo stereoselective appr…
Bridge-Clamp Bis(tetrazine)s with [N] 8 π-Stacking Interactions and Azido- s -Aryl Tetrazines: Two Classes of Doubly Clickable Tetrazines
2020
Click chemistry at a tetrazine core is useful for bioorthogonal labeling and crosslinking. Introduced here are two new classes of doubly clickable s-aryl tetrazines synthesized by Cu-catalyzed cross-coupling. Homocoupling of o-brominated s-aryl tetrazines leads to bis(tetrazine)s structurally characterized by tetrazine cores arranged face-to-face. [N]8 π-stacking interactions are essential to the conformation. Upon inverse electron demand Diels-Alder (iEDDA) cycloaddition, the bis(tetrazine)s produce a unique staple structure. The o-azidation of s-aryl tetrazines introduces a second proximal intermolecular clickable function that leads to double click chemistry opportunities. The stepwise i…
Polar [3 + 2] cycloaddition of ketones with electrophilically activated carbonyl ylides. Synthesis of spirocyclic dioxolane indolinones
2008
International audience; The [3 + 2] cycloaddition reaction between carbonyl ylides generated from epoxides and ketones (ethyl pyruvate, ethyl phenylglyoxylate, isatin, N-methylisatin and 5-chloroisatin) to give substituted dioxolanes and spirocyclic dioxolane indolinones was investigated. The effect of microwave irradiation on the outcome of the reaction was studied. The thermal reaction between 2,2-dicyano-3-phenyloxirane and N-methylisatin was theoretically studied using DFT methods. This reaction is a domino process that comprises two steps. The first is the thermal ring opening of the epoxide to yield a carbonyl ylide intermediate, whereas the second step is a polar [3 + 2] cycloadditio…
An alternative route to 2H-naphtho[1,2-b]thiete and its cycloaddition products
1998
2-(1H-Benzotriazol-1-ylmethyl)-1-naphthalenol (1) can be transformed in high yields to the corresponding thiol 4. Flash vacuum pyrolysis of 4 leads to 2H-naphtho[1,2-b]thiete (5). The benzotriazolyl group proved to be a good leaving group; however, a subsequent nitrogen extrusion takes place under flash vacuum pyrolysis conditions and cyclopentadienecarbonitriles 6a,b are formed by a ring contraction (Scheme 1). Cycloaddition reactions of 5 and dienophiles or heterodienophiles yield the naphtho-condensed sulfur heterocycles 8, 10, 12 and 14 (Scheme 2).
Cycloaddition reactions of benzothiete with azomethines
1986
Obtention de diaryl-2,3 dihydro-3,4 benzothiazines-1,3 (70%) via la cycloaddition de la thiobenzoquinone methode-1,2 (obtenue par scission thermique du benzothiete) et d'arylimines de benzaldehydes. Obtention egalement de 10% du dimere (dibenzo [b, f] dithiocinne-1,5)
A DFT Study of the Domino Inter [4 + 2]/Intra [3 + 2] Cycloaddition Reactions of Nitroalkenes with Enol Ethers
2000
The molecular mechanism of the domino inter [4 + 2]/intra [3 + 2] cycloaddition reactions of nitroalkenes with enol ethers to give nitroso acetal adducts has been characterized using density functional theory methods with the B3LYP functional and the 6-31G* basis set. The presence of Lewis acid catalyst and solvent effects has been taken into account to model the experimental environment. These domino processes comprise two consecutive cycloaddition reactions: the first one is an intermolecular [4 + 2] cycloaddition of the enol ether to the nitroalkene to give a nitronate intermediate, which then affords the final nitroso acetal adduct through an intramolecular [3 + 2] cycloaddition reacti…
ChemInform Abstract: Cycloaddition of Benzothiete and Electron-Deficient Nitriles.
2010
The o-quinoid 8π electron system 2, generated by thermal ring opening of benzothiete (1), enters regio-specific [8π + 2π] cycloaddition reactions with electron-deficient nitriles 3a-d, yielding the 4H-1,3-benzothiazines 4a-d. A competitive dimerization of 1 leads to 1,5-dibenzo[b,f]dithiocin (5). Depending on the nitrile further competitive or subsequent reactions (2 + 3b 7b, 2 + 3d 4d 8d) can occur. The cycloadducts 10e and 11e gained from 3e anticipate a primary cleavage of 3e to methylisothiocyanate 9e which reacts at the CN double bond as well as at the CS double bond.
Cycloaddition of benzothiete and electron-deficient nitriles
1991
The o-quinoid 8π electron system 2, generated by thermal ring opening of benzothiete (1), enters regio-specific [8π + 2π] cycloaddition reactions with electron-deficient nitriles 3a-d, yielding the 4H-1,3-benzothiazines 4a-d. A competitive dimerization of 1 leads to 1,5-dibenzo[b,f]dithiocin (5). Depending on the nitrile further competitive or subsequent reactions (2 + 3b 7b, 2 + 3d 4d 8d) can occur. The cycloadducts 10e and 11e gained from 3e anticipate a primary cleavage of 3e to methylisothiocyanate 9e which reacts at the CN double bond as well as at the CS double bond.
Neue Diels-Alder-Reaktionen von 1-Methylpyrano[3,4-b]indol-3(9H)-on mit cyclischen CC-Dienophilen: ein einfacher Zugang zu [b]anellierten Carbazol-De…
1988
1-Methylpyrano[3,4-b]indol-3(9H)-on (1) reagiert als synthetisches Aquivalent von Indolo-2,3-chinodimethan mit Arin, p-Benzochinon und p-Naphthochinon zu neuen [b]anellierten Carbazol-Derivaten. Durch das Reaktionsmedium bedingt lassen sich bei der Cycloaddition von 1 mit Arin zugleich auch mononitrierte Carbazole isolieren. New Diels-Alder Reactions of 1-Methylpyrano[3,4-b]indol-3(9H)-one with Cyclic CC-Dienophiles: A Simple Way to [b]Annulated Carbazole Derivatives. 1-Methylpyrano[3,4-b]indol-3-(9H)-one (1) reacts as synthetic equivalent of indolo-2,3-quinodimethane with benzyne, p-benzoquinone, and p-naphthoquinone to give new [b]annulated carbazole derivatives. In the Diels-Alder reacti…