FORMATION OF CARBONYL YLIDE BY THE INTRAMOLECULAR CARBENIC REACTION. DISROTATORY RING CLOSURE OF CARBONYL YLIDE TO EPOXIDE

1976 ◽  
Vol 5 (3) ◽  
pp. 233-234 ◽  
Author(s):  
Toshikazu Ibata
Keyword(s):  
Ring Closure ◽  
Carbonyl Ylide

Epoxide of a ketene acetal. The first 2,2-dialkoxyoxirane to be isolated

2001 ◽  
Vol 79 (2) ◽  
pp. 110-113 ◽  
Author(s):  
Malgorzata Dawid ◽  
Paul C Venneri ◽  
John Warkentin
Keyword(s):  
Ir Spectroscopy ◽  
Carbonyl Group ◽  
Ring Closure ◽  
Nucleophilic Attack ◽  
Carbonyl Carbon ◽  
Subsequent Formation ◽  
H Nmr ◽  
Carbonyl Ylide ◽  
Ketene Acetal ◽  
C Nmr

Dimethoxycarbene, generated at 110°C in benzene by thermolysis of 2,2-dimethoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline, reacted with cyclohexanone to afford 2,2-dimethoxyspiro[2.5]-1-oxaoctane. It is the first oxirane of a ketene acetal that could be isolated and characterized by 1H NMR-, 13C NMR-, and IR spectroscopy. The identical oxirane might be expected from conrotatory cyclization of the appropriate carbonyl ylide. That ylide was generated under identical conditions by thermolysis of an oxadiazoline precursor (3,4-diaza-2,2-dimethoxy-1-oxaspiro[4.5]dec-3-ene) (14). The ylide could either cyclize or fragment to dimethoxycarbene and cyclohexanone. Addition of 4-tert-butylcyclohexanone, to trap dimethoxycarbene in competition with the cyclohexanone generated from 14 and, to leave the ylide closure pathway as the only route to the oxirane, showed that the carbonyl ylide does cyclize. However, fragmentation of the carbonyl ylide is relatively fast compared to its cyclization and most of it fragments to dimethoxycarbene and cyclohexanone. Oxirane formation from the carbene and ketone is probably either a concerted cycloaddition or it occurs in two steps, by nucleophilic attack at the carbonyl carbon to form the C—C bond first, prior to ring closure. If the carbene is bonded first to O of the carbonyl group, as it is in the carbonyl ylide, subsequent formation of the C—C bond is too slow, relative to fragmentation of the ylide, to afford the oxirane ring efficiently.Key words: carbonyl ylide, dialkoxyoxirane, dimethoxycarbene, oxadiazoline, oxirane.

Carbonyl Ylides and the Rearrangement of (+)-trans-2,3-Diisopropenyloxirane

1974 ◽  
Vol 52 (11) ◽  
pp. 2098-2101 ◽  
Author(s):  
Jean-Claude Paladini ◽  
R. J. Crawford
Keyword(s):  
Gas Phase ◽  
Kinetic Data ◽  
Ring Opening ◽  
Ring Closure ◽  
Carbonyl Ylide ◽  
Kinetics Of ◽  
Oxygen Bond

The kinetics of the gas phase racemization and rearrangement of 2,3-diisopropenyloxirane have been determined. Comparison with the kinetic data for 2,3-divinyloxirane allows us to exclude the mechanism for the formation of vinyldihydrofuran wherein an inward conrotatory ring opening comprises the first step. The mechanism proposed consists of an isomerization about the carbon–oxygen bond of the carbonyl ylide to form an isomeric intermediate which then undergoes a disrotatory five-centered ring closure to produce 2-isopropenyl-4-methyl-2,3-dihydrofuran.

Ring Closure Matrix

2015 ◽  
Vol 19 (3) ◽  
pp. 274-281
Author(s):  
Milan Randic ◽  
Marjana Novic ◽  
Dejan Plavsic
Keyword(s):  
Ring Closure

A new heterocyclic ring closure in ferricyanide oxidation of 2,4,6-triphenylpyridinium salts

1983 ◽  
Vol 48 (11) ◽  
pp. 3307-3314 ◽  
Author(s):  
Petr Nesvadba ◽  
Petr Štrop ◽  
Josef Kuthan
Keyword(s):  
Alkaline Solution ◽  
Heterocyclic Ring ◽  
Potassium Ferricyanide ◽  
Probable Mechanism ◽  
Ring Closure ◽  
Pyridinium Salts ◽  
Mechanism Of Formation ◽  
Pyrrole Derivatives ◽  
Quaternary Pyridinium Salts ◽  
Heterocyclic Derivatives

The quaternary pyridinium salts Ia-Ic react with alkaline solution of potassium ferricyanide to give the condensed heterocyclic derivatives IIIa, b, IV, whereas the salts Id-If give the pyrrole derivatives IIa-IIc under the same conditions. The diaza heterocycle IIIa reacts with methyl iodide to give methoiodide V, whereas by action of bromine it produces two monobromo derivatives VIa, b. The pyrrole derivatives IIa, b give monobromo derivatives IId, e on bromination. A probable mechanism of formation of the heterocyclic derivatives is discussed.

XXI.—The Synthesis of Some Methyl- and Dimethylfluoranthenes

1972 ◽  
Vol 69 (4) ◽  
pp. 281-286
Author(s):  
H. F. Andrew ◽  
Neil Campbell ◽  
E. M. Swan ◽  
N. H. Wilson
Keyword(s):  
Benzene Ring ◽  
Propionic Acid ◽  
Hydrofluoric Acid ◽  
Phenyl Ring ◽  
Ring Closure ◽  
Methyl Group ◽  
Image Position

3-Methylfluorene-9-propionic acid (1) with hydrofluoric acid undergoes ring-closure on the substituted ring to give 1,2,3,10b-tetrahydro-5-methylfluoranthen-3-one (II).Wolff-Kishner reduction of the ketone yielded l,2,3,10b-tetrahydro-5-methylfluoranthene which on dehydrogenation gave 2-methylfluoranthene (III, R=H) identical with a sample prepared according to the method of Tucker (1952) and differing from 8-methylfluoranthene. This proved that ring-closure of (I) had occurred as expected on the methyl-bearing benzene ring. In this instance ring-closure occurs in the position meta to the methyl group and is reminiscent of the similar ring-closure of 2-phenyl-2-p-tolylpropionic acid to give 6-methyl-3-phenylindanone (Pfeiffer and Roos 1941). It thus provided a further example of the limitations of von Braun's statement that Friedel-Crafts ring-closure occurs much less readily at the position meta to a methyl group than on a phenyl ring (von Braun, Manz and Reinsch 1928).

scholarly journals Structures of Rhodopseudomonas palustris RC-LH1 complexes with open or closed quinone channels

2021 ◽  
Vol 7 (3) ◽  
pp. eabe2631
Author(s):  
David J. K. Swainsbury ◽  
Pu Qian ◽  
Philip J. Jackson ◽  
Kaitlyn M. Faries ◽  
Dariusz M. Niedzwiedzki ◽  
...  
Keyword(s):  
Binding Sites ◽  
Rhodopseudomonas Palustris ◽  
Ring Closure ◽  
Light Harvesting Complex ◽  
The Core ◽  
Quinone Binding ◽  
Cryo Electron Microscopy ◽  
Unique Protein ◽  
Center Light ◽  
Resolution Structure

The reaction-center light-harvesting complex 1 (RC-LH1) is the core photosynthetic component in purple phototrophic bacteria. We present two cryo–electron microscopy structures of RC-LH1 complexes from Rhodopseudomonas palustris. A 2.65-Å resolution structure of the RC-LH114-W complex consists of an open 14-subunit LH1 ring surrounding the RC interrupted by protein-W, whereas the complex without protein-W at 2.80-Å resolution comprises an RC completely encircled by a closed, 16-subunit LH1 ring. Comparison of these structures provides insights into quinone dynamics within RC-LH1 complexes, including a previously unidentified conformational change upon quinone binding at the RC QB site, and the locations of accessory quinone binding sites that aid their delivery to the RC. The structurally unique protein-W prevents LH1 ring closure, creating a channel for accelerated quinone/quinol exchange.

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