Generation and trapping of a silyloxy carbonyl ylide

Sharma, Pradecp K.; Warkentin, John

doi:10.1016/0040-4039(95)01591-5

Cited by 18 publications

(4 citation statements)

References 26 publications

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“…There is now some evidence for the intermediacy of carbonyl ylides from thermolysis of oxadiazolines. That evidence includes trapping reactions 33 and the formation of compounds that must have come from cyclization of an ylide (Scheme 7, for example). 16c The fact that the carbonyl ylides, with some exceptions, 33 are not readily trapped under the reaction conditions probably means that they fragment easily, especially in cases that lead to a carbene that is relatively stable as a singlet.…”

Section: Sigmatropic H-shift (Scheme 6)mentioning

confidence: 99%

Δ3-1,3,4-Oxadiazolines.† Versatile sources of reactive intermediates

Warkentin

2000

J. Chem. Soc., Perkin Trans. 1

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Section: Sigmatropic H-shift (Scheme 6)mentioning

confidence: 99%

Δ3-1,3,4-Oxadiazolines.† Versatile sources of reactive intermediates

Warkentin

2000

J. Chem. Soc., Perkin Trans. 1

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“…Δ 3 -1,3,4-Oxadiazolines are popular and versatile sources of free carbenes that can be liberated by either photolysis or thermolysis. − ,− The diastereomeric precursors r - 10 and s - 10 were used separately herein to generate carbene 1 (Figure ). They were dissolved in either PhC(O)H or PhC(O)Me and heated to T = 165 °C until fully decomposed (Scheme ).…”

Section: Results and Discussionmentioning

confidence: 99%

“…are popular and versatile sources of free carbenes that can be liberated by either photolysis or thermolysis [71][72][73][98][99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114][115]. The diastereomeric precursors r-10 and s-10 were used separately herein to generate carbene 1(Figure 4).…”

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confidence: 99%

Intermolecular Reactions of a Foiled Carbene with Carbonyl Compounds: The Effects of Trishomocyclopropyl Stabilization

et al. 2015

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endo-Tricyclo[3.2.1.0(2,4)]oct-8-ylidene is a foiled carbene reaction intermediate. It was generated by thermolyzing Δ(3)-1,3,4-oxadiazoline precursors dissolved in benzaldehyde and acetophenone. The products appear to stem from direct insertion of the carbene's divalent C atom into the α-bonds of the carbonyl compounds; however, this is only superficial. The strict stereochemistry observed is due to the topologies of the reaction intermediates of the proposed two-step mechanism. Bimolecular nucleophilic addition generates bent 1,3-zwitterions. The neutral reaction intermediates undergo pinacolic rearrangements to form the observed adducts. Product ratios reflect the migratory aptitudes of the carbonyl compounds' α-substituents. The carbene reaction was modeled using DFT. The singlet carbene's bicoordinate C atom bends 31° toward the endo-fused cyclopropane bond, elongating it to r = 1.69 Å. The resulting trishomocyclopropyl HOMO{-1} is a three-center two-electron bond responsible for the electron-deficient carbene's nucleophilicity. Its calculated properties are consistent with this assertion: (1) singlet-triplet (ΔE(S-T)) energy gap of -25 kcal/mol, (2) gas-phase proton affinity (PA) value of 272 kcal/mol, (3) hard and soft acid and base (HSAB) ΔN value of -0.2 in its initial reaction with the carbonyl compounds, and (4) negative frontier orbital interaction values ΔΔE(PhC(O)H) = -4.38 eV and ΔΔE(PhC(O)Me) = -3.97 eV.

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“…15 ) of Scheme 4 for dioxycarbenes, and according to Scheme 5 for alkoxyaminocarbenes (Ref. [17][18][19][20], and that mechanism is assumed to apply in the absence of evidence to the contrary. In a subsequent step the ylide fragments to carbene and carbonyl compound, Scheme…”

Section: Introductionmentioning

confidence: 99%