Ketene acetals from thermolysis of aryloxy methoxy oxadiazolines. Evidence for carbonyl ylide intermediates

1997 ◽  
Vol 75 (3) ◽  
pp. 326-332 ◽  
Author(s):  
Philippe Couture ◽  
Manal El-Saidi ◽  
John Warkentin
Keyword(s):  
Pure Form ◽  
Second Step ◽  
Carbonyl Ylide ◽  
Ketene Acetal ◽  
Ketene Acetals

Thermolysis of oxadiazolines (5) in benzene at 110 °C leads to ketene acetals (11) as minor products. Carbonyl ylide intermediates (6), and oxiranes (7), presumably in equilibrium with those ylides, are implicated as unstable precursors of the ketene acetals although none of the oxiranes (carbonyl protected α-lactones) were isolable and only one of the ketene acetals was isolable in pure form. The evidence points to the two-step sequence of thermolysis of oxadiazolines, namely, initial cycloreversion to N2 and carbonyl ylide (6), rather than concerted fragmentation to N2, acetone, and carbene (12). The first-formed ylide does fragment to carbene and acetone in a second step that competes with oxirane formation. A tentative mechanism for reaction of 7 with 12, to afford 11, is advanced. Keywords: carbonyl ylide, dioxy oxirane, ketene acetal, oxadiazoline.

Synthèse totale des acides (+) et (–) nonactique à partir de carbohydrates

1981 ◽  
Vol 59 (3) ◽  
pp. 572-583 ◽  
Author(s):  
Robert E. Ireland ◽  
Jean-Paul Vevert
Keyword(s):  
Carbon Atom ◽  
Absolute Configuration ◽  
Claisen Rearrangement ◽  
Sigmatropic Rearrangement ◽  
Chiral Carbon ◽  
Ketene Acetal ◽  
Boat Form ◽  
Aliphatic Esters ◽  
Ketene Acetals

The synthesis of (−) and (+) nonactic acids (2a) and (2b) has been achieved starting from D-mannose (7) and D-gluono-γ-lactone (22) respectively. The key step in the synthesis is the [3,3]-sigmatropic rearrangement of the silylated ketene-acetals IV leading to control of the C-2 configuration of nonactic acid. The ketene-acetals were prepared from aliphatic esters of furanoid-glycals II, which were prepared in ten steps from the carbohydrate precursor. The chiral sites of the glycals arise from the corresponding centres in the starting monosaccharide. This type of ketene-acetal Claisen rearrangement leads to products containing the aldol portion required. At the same time knowledge of the absolute configuration of the chiral carbon atom of nonactic acid allows for the determination of the chair or boat form of the transition state of the [3,3]-sigmatropic rearrangement. [Journal translation]

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.

Diaryloxycarbenes from oxadiazolines

2001 ◽  
Vol 79 (3) ◽  
pp. 319-327
Author(s):  
Xiaosong Lu ◽  
Darren L Reid ◽  
John Warkentin
Keyword(s):  
Acidic Solution ◽  
Benzene Solution ◽  
Subsequent Treatment ◽  
Oxidative Cyclization ◽  
Lead Tetraacetate ◽  
Dimethyl Acetylenedicarboxylate ◽  
Mild Conditions ◽  
Product Mixture ◽  
Carbonyl Ylide ◽  
Ketene Acetal

Symmetric and unsymmetric 2,2-diaryloxy-5,5-dimethyl-Δ3-1,3,4-oxadiazolines were synthesized by oxidative cyclization of aryloxycarbonyl hydrazones of acetone with lead tetraacetate and subsequent treatment of the product mixture with a phenol in acidic solution. Thermolysis of the oxadiazolines in benzene solution at 110°C afforded carbonyl ylide intermediates that cyclize, in part, to the corresponding 2,2-diaryloxyoxirane intermediates. The oxiranes, which were not observed, are required to account for the 1,1-diaryloxy-2-methylpropenes (ketene acetals) that were isolated. Most of the carbonyl ylides fragment to acetone and diaryloxycarbenes. The latter form dimers (tetraaryloxyethenes) or they can be trapped with phenols to form orthoformates. Diphenoxycarbene was also trapped with dimethyl acetylenedicarboxylate (DMAD). The method appears to be the first for generating the parent diphenoxycarbene under relatively mild conditions in solution, and the only one to date for generating unsymmetrically substituted diaryloxycarbenes. Minor competing fragmentations of the oxadiazolines to 2-diazopropane and the appropriate diaryl carbonates, were also observed.Key words: diarylcarbonate, diaryloxycarbene, diaryloxy oxadiazoline, ketene acetal, orthoformate.

A comprehensive kinetic study of the conventional free-radical polymerization of seven-membered cyclic ketene acetals

2017 ◽  
Vol 8 (34) ◽  
pp. 5139-5147 ◽  
Author(s):  
Antoine Tardy ◽  
Jean-Claude Honoré ◽  
Didier Siri ◽  
Julien Nicolas ◽  
Didier Gigmes ◽  
...  
Keyword(s):  
Free Radical ◽  
Kinetic Study ◽  
Kinetic Analysis ◽  
Radical Polymerization ◽  
Free Radical Polymerization ◽  
Ketene Acetal ◽  
Cyclic Ketene Acetals ◽  
Ketene Acetals

The current study reports on the kinetic analysis of the free-radical polymerization of several seven-membered cyclic ketene acetal monomers.

Ketene Acetals. XIV. The Reactions of Ketene Acetal with Quinones

1944 ◽  
Vol 66 (7) ◽  
pp. 1077-1083 ◽  
Author(s):  
S. M. McElvain ◽  
Edward L. Engelhardt
Keyword(s):  
Ketene Acetal ◽  
Ketene Acetals

Temperature Dependence of the Critical Electron Dose for Fatty Acid Monolayers

1982 ◽  
Vol 40 ◽  
pp. 78-79
Author(s):  
Kenneth H. Downing ◽  
Robert M. Glaeser
Keyword(s):  
Electron Beam ◽  
Fatty Acid ◽  
Inelastic Scattering ◽  
Temperature Dependence ◽  
Structural Damage ◽  
Direct Result ◽  
Second Step ◽  
Strong Temperature Dependence ◽  
Electron Dose ◽  
Covalent Bonds

The structural damage of molecules irradiated by electrons is generally considered to occur in two steps. The direct result of inelastic scattering events is the disruption of covalent bonds. Following changes in bond structure, movement of the constituent atoms produces permanent distortions of the molecules. Since at least the second step should show a strong temperature dependence, it was to be expected that cooling a specimen should extend its lifetime in the electron beam. This result has been found in a large number of experiments, but the degree to which cooling the specimen enhances its resistance to radiation damage has been found to vary widely with specimen types.

Sign in / Sign up

Export Citation Format

Share Document