Photolysis of 2-alkoxy-.DELTA.3-1,3,4-oxadiazolines. A new route to diazoalkanes

Majchrzak, Michał; Bekhazi, Michel; Tse-Sheepy, Irene; Warkentin, John

doi:10.1021/jo00269a019

Cited by 57 publications

(31 citation statements)

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“…Tricyclo[6.2.1.0 2,7 ]undec-9-en-11-ylidene (5) is a typical foiled carbene based on a cyclopent-3-enylidene scaffold. In these reactive intermediates, stabilization occurs mainly through electron donation from the C=C double bond into the antibonding lone pair (LP*) of the divalent carbon atom, making the LUMO of carbene 5 less reactive.…”

Section: Resultsmentioning

confidence: 99%

“…[2] The only drawback of precursor 1 was that the two diastereomers, which are formed in about equal amounts, decomposed differently, especially when photolyzed. Whereas diastereomer 1a can be conveniently decomposed within two hours, diastereomer 1b requires reaction times of more than one day.…”

Section: -Methoxy-2-methyl-∆mentioning

confidence: 99%

“…Photolysis of 1a in pure methanol afforded two methyl ethers: 48 % anti,endo-11-methoxytricyclo[6.2.1.0 2,7 ]undec-9-ene (10me) and 43 % 3-methoxytricyclo[5.4.0.0 2,6 ]undec-4-ene (12me) ( Table 1, Scheme 2). The presence of the rearrangement product 12me suggests that syn-diazonium ion 3 has been generated as an intermediate [6b] and that the reaction mainly does not proceed through carbene 5.…”

Section: -Methoxy-2-methyl-∆mentioning

confidence: 99%

“…[1] Especially, 2-alkoxy-∆ 3 -1,3,4-oxadiazolines are very attractive since Warkentin has shown some 20 years ago that they are suitable for the generation of alkyl carbenes under photochemical conditions after prior formation of a diazoalkane. [2] Indeed, they have permitted numerous investigations. [3] In this work, we will show that the two diastereomers of oxadiazoline 1 differ significantly in their chemistry, that their thermal activation leads exclusively to the formation of the strained alkenylidene 5 without the intermediacy of a diazo species, and that the generated intermediates are very efficiently trapped by alcohols.…”

Section: Introductionmentioning

confidence: 99%

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2‐Methoxy‐Δ³‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

et al. 2008

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In the course of our investigation of the intermolecular reactions of foiled carbenes of the norborn-2-en-7-ylidene type, we have investigated the decomposition of methoxyoxadiazoline 1 in alcohols. Most of the reactions performed lead to products with an anti configuration confirming the participation of the double bond to the stabilization of the transition states. The thermal behavior of spirooxadiazoline 1 is quite different from the behavior of the parent 2-methoxy-2,5,5-trimethyl-∆ 3 -1,3,4-oxadiazoline. Photolysis of 1 leads to the carbene after prior formation of the diazo compound whereas thermolysis cleanly generates an extremely unstable carbonyl ylide 4 that immediately decomposes to the stabilizednucleophilic carbene 5 and methyl acetate without genera-

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Section: Resultsmentioning

confidence: 99%

Section: -Methoxy-2-methyl-∆mentioning

confidence: 99%

Section: -Methoxy-2-methyl-∆mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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2‐Methoxy‐Δ³‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

et al. 2008

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“…The solvent was removed under vacuum and the residue was recrystallized. The acetyl hydrazone of pinacolone ( l e ) was obtained by refluxing a solution of acetylhydrazine in excess pinacolone for 20 h. Excess pinacolone was distilled off and the residue was recrystallized (12). New acetylhydrazones are reported below.…”

Section: Generalmentioning

confidence: 99%

Thermolysis of 2-acyloxy-Δ³-1,3,4-oxadiazolines. Evidence for a preferred sense of cycloreversion to carbonyl ylides and for fast 1,4-sigmatropic ylide rearrangement

Majchrzak¹,

Warkentin²

1989

Can. J. Chem.

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Thermolysis of 2-acyloxy-2,5,5-trialkyl-A3-1 ,3,4-oxadiazolines in benzene solution at 80°C furnishes acyloxy-substituted en01 ethers (hemiacylals) in high yield. Mixtures of cis:trans isomers of such oxadiazolines afford mixtures of isomeric hemiacylals in nearly the same ratio. Those and other results are rationalized in terms of cycloreversion of the oxadiazolines to carbonyl ylides that are not equilibrated during their lifetimes and undergo primarily 1,4-sigmatropic H-migration. Some fragmentation of the ylides to anhydrides and carbenes was also observed. A consistent mechanistic account includes concerted suprafacial (415 + 215) cycloreversion in the sense that places a large ylide substituent at C-l or at C-3, preferentially exo.A smaller preference for the cycloreversion that places the acetoxy group at C-1 in the endo position, when the steric effect of the alkyl group at C-1 is small, can be inferred. The possibility that the overall 1,4-H shift is the result of sequential 1,7-antarafacial and 1,4-suprafacial shifts, in some cases, is considered.Key words: carbonyl ylide; 1,4-sigmatropic rearrangement; cycloreversion, thermal, of oxadiazolines; ylide, carbonyl; oxadiazoline, thermolysis of. [Traduit par la revue] Introduction 1,4-Sigmatropic H-migrations (1) in ylides, including azomethine ylides (2-4) and carbonyl ylides (5-7), are well known. Many details of those rearrangements, however, are poorly understood. First, there is the question of whether ylide equilibration, by rotation about one or both carbon-heteroatom bonds, is faster or slower than sigmatropic rearrangement. Second, the preferred geometry (E or 2 ) about the newly formed double bond of the product of H-migration is not known. Third, the sense of sigmatropic rearrangement (toward C-1 or C-3) in unsymmetric systems is not established for a variety of cases. Finally, there is little information in the literature concerning substitution patterns that cause suppression of the sigmatropic rearrangement in favour of alternative unimolecular processes such as fragmentations to carbonyl compounds and carbenes.These questions are illustrated in Scheme 1 for a simple carbonyl ylide to which they would apply.We now report the synthesis and thermolysis of a series

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Dimethyl Acetylenedicarboxylate

Stelmach¹,

Winkler²

2001

Encyclopedia of Reagents for Organic Synthesis

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Photolysis of 2-alkoxy-.DELTA.3-1,3,4-oxadiazolines. A new route to diazoalkanes

Cited by 57 publications

References 1 publication

2‐Methoxy‐Δ³‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

2‐Methoxy‐Δ³‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

Thermolysis of 2-acyloxy-Δ³-1,3,4-oxadiazolines. Evidence for a preferred sense of cycloreversion to carbonyl ylides and for fast 1,4-sigmatropic ylide rearrangement

Dimethyl Acetylenedicarboxylate

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Photolysis of 2-alkoxy-.DELTA.3-1,3,4-oxadiazolines. A new route to diazoalkanes

Cited by 57 publications

References 1 publication

2‐Methoxy‐Δ3‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

2‐Methoxy‐Δ3‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

Thermolysis of 2-acyloxy-Δ3-1,3,4-oxadiazolines. Evidence for a preferred sense of cycloreversion to carbonyl ylides and for fast 1,4-sigmatropic ylide rearrangement

Dimethyl Acetylenedicarboxylate

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2‐Methoxy‐Δ³‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

2‐Methoxy‐Δ³‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

Thermolysis of 2-acyloxy-Δ³-1,3,4-oxadiazolines. Evidence for a preferred sense of cycloreversion to carbonyl ylides and for fast 1,4-sigmatropic ylide rearrangement