On the regioselectivity of Wittig reactions with unsymmetrically substituted succinic anhydrides

1989 ◽  
Vol 67 (9) ◽  
pp. 1401-1410 ◽  
Author(s):  
Margaret M. Kayser ◽  
Livain Breau
Keyword(s):  
Oxygen Atom ◽  
Transition State ◽  
Carbonyl Group ◽  
Wittig Reaction ◽  
Cyclic Anhydrides ◽  
Wittig Reactions ◽  
Deficient Phosphorus

Phosphorane ylids react readily with succinic anhydrides to give enol-lactones. With highly substituted succinic anhydrides, condensations occur at the less substituted carbonyl group, suggesting that the reaction is sterically controlled. This, however, is not the case in monosubstituted anhydrides where effects other than steric become dominant. Condensation of phosphorane 1a with methoxysuccinic anhydride occurs selectively at the carbonyl group adjacent to the substituent. Stabilization of the transition state through complexation between the oxygen atom of the substituent and an electron-deficient phosphorus of the ylid is proposed. Keywords: cyclic anhydrides, Wittig reaction, regioselectivity, stabilized ylid.

On the regioselectivity of the condensation of stabilized phosphoylids with 3-substituted phthalic anhydrides

1989 ◽  
Vol 67 (4) ◽  
pp. 569-573 ◽  
Author(s):  
Livain Breau ◽  
Margaret M. Kayser
Keyword(s):  
Oxygen Atom ◽  
Transition State ◽  
Carbonyl Group ◽  
Lewis Base ◽  
Carbonyl Function ◽  
Deficient Phosphorus ◽  
Phthalic Anhydrides

Condensations of stabilized phosphorane 1 with 3-substituted phthalic anhydrides were investigated. The importance of various effects influencing regio- and stereoselectivity of these reactions is discussed. It is proposed that the oxygen atom on the substituents in position 3 can act as a Lewis base toward the electron-deficient phosphorus of the ylid. The resulting complexation stabilizes the transition state for the reaction at the ortho carbonyl group, thus offsetting the usual steric and "push" effects, which favour attack at the meta carbonyl function. Keywords: Wittig condensations, phthalic anhydrides, regioselectivity, stereoselectivity.

On the synthesis and the mechanism of formation of halogenated enol lactones

1997 ◽  
Vol 75 (10) ◽  
pp. 1322-1330 ◽  
Author(s):  
Margaret M. Kayser ◽  
Jun Zhu ◽  
Donald L. Hooper
Keyword(s):  
Reaction Mechanism ◽  
Organic Synthesis ◽  
Wittig Reaction ◽  
Biological Properties ◽  
Mechanism Of Formation ◽  
Direct Route ◽  
Cyclic Anhydrides ◽  
Wittig Reactions

The synthesis of halo enol lactones from cyclic anhydrides via lactonization of the corresponding keto phosphoranes provides a direct route to these interesting compounds, which possess important biological properties and are useful intermediates in organic synthesis. In this paper we outline the syntheses of several halo enol lactones and discuss mechanistic consequences of these reactions on the understanding of Wittig reactions with cyclic anhydrides. Keywords: halolactonization, cyclic anhydrides, halo enol lactones, Wittig reaction mechanism.

On the mechanism of Wittig reactions with cyclic anhydrides. II.

1993 ◽  
Vol 71 (7) ◽  
pp. 1010-1021 ◽  
Author(s):  
Margaret M. Kayser ◽  
Krista L. Hatt ◽  
Heshui Yu ◽  
Donald L. Hooper
Keyword(s):  
Transition State ◽  
Low Energy ◽  
Spectroscopic Methods ◽  
Selective Transformation ◽  
Π Stacking ◽  
Wittig Olefination ◽  
Reversible Formation ◽  
Cyclic Anhydrides ◽  
Wittig Reactions

A study by NMR spectroscopic methods and trapping experiments of the mechanism of Wittig reactions between stabilized phosphoranes and unsymmetrically substituted cyclic anhydrides suggests that two reactions are involved: (1) a low-energy, reversible formation of acyclic adducts; and (2) a higher energy "Wittig olefination" reaction leading to enol-lactones. The latter, more selective, transformation requires a more highly organized transition state in which π-stacking and stabilizing complexations are important factors.

Synthesis of 8-HEPE and 10-HDoHE in both (R)- and (S)-Forms via Wittig Reactions with COOH-Ylides

Synlett ◽  
2019 ◽  
Vol 30 (03) ◽  
pp. 338-342
Author(s):  
Yuta Suganuma ◽  
Shun Saito ◽  
Yuichi Kobayashi
Keyword(s):  
Docosahexaenoic Acid ◽  
Eicosapentaenoic Acid ◽  
Wittig Reaction ◽  
Phosphonium Salt ◽  
Wittig Reactions

Wittig reactions using carboxy (CO2H) ylides derived from a carboxylic phosphonium salt and NaN(TMS)2 (NaHMDS) in a 1:1 ratio were applied to the synthesis of 8-HEPE and 10-HDoHE, which are metabolites of eicosapentaenoic acid and docosahexaenoic acid, respectively. The attempted Wittig reaction of 3-(TBS-oxy)pentadeca-4E,6Z,9Z,12Z-tetraenal with the carboxy ylide (2 equiv) derived from Br– Ph3P+(CH2)4CO2H and NaHMDS (1:1) competed with the elimination of the TBS-oxy group at C3 to give a mixture of the Wittig product and the elimination product in 45–50% and 30–40% yields, respectively. The elimination was suppressed completely by using three equiv of the carboxy ylides in THF/HMPA (7–8:1), and the subsequent desilylation gave 8-HEPE in (R)- and (S)-forms. Similarly, both enantiomers of 10-HDoHE were synthesized.

Crystal structures of highly stabilized ylides: methyl(3-methoxy,2-methoxycarbonylbenzoyl) triphenyl- phosphoranylideneacetate and methyl(2-methoxycarb-6-nitrobenzoyl)triphenyl phos phoranyl ideneacetate and the salt methyl(triphenylphosphoranylidene)acetate tetrafluoroborate

1998 ◽  
Vol 76 (12) ◽  
pp. 1844-1852
Author(s):  
Fernande D Rochon ◽  
Robert Melanson ◽  
Margaret M Kayser
Keyword(s):  
Key Words ◽  
Crystal Structures ◽  
Nitro Derivative ◽  
Transient Species ◽  
X Ray Diffraction ◽  
X Ray ◽  
Ionic Salt ◽  
Higher Temperature ◽  
Cyclic Anhydrides ◽  
Wittig Reactions

At lower temperatures stabilized ylides react with unsymmetrically substituted phthalic anhydrides to give two acyclic adducts. When the reactions are allowed to proceed at higher temperature enol lactones are formed. Identification of the acyclic intermediates was necessary to understand the mechanism of these Wittig reactions. The transient species trapped in the reaction with trimethyloxonium tetrafluoroborate were unambiguously identified by crystallographic methods. The crystal structures of the tetrafluoroborate salt of methyl(triphenylphosphoranyl idene)- acetate (8), methyl(3-methoxy,2-methoxycarbonylbenzoyl)triphenylphosphoranylideneacetate (6β), and methyl(2-methoxycarbonyl,6-nitrobenzoyl)triphenylphosphoranylideneacetate (7α) were studied by X-ray diffraction. The ionic salt (8) is monoclinic, P21c,a= 12.640(5), b = 13.945(9), c = 14.825(6) Å, β = 125.32(3)°, Z = 4, and R = 0.065 (F >5.4 σ(F)). Crystal 6 β is monoclinic, P21c,a = 16.391(16), b = 9.029(6), c = 19.835(19) Å, β = 116.60(6)°, Z = 4, and R = 0.070 (F > 4.6 σ(F)), while crystal 7α is also monoclinic, P21c,a = 9.513(5), b = 9.361(3), c = 30.908(13) Å, β = 98.42(3)°, Z = 4, and R = 0.057 (F >5 σ(F)). In the BF 4- salt (12), the four P-C distances are equal (1.791(5)-1.801(7) Å) with identical tetrahedral angles. For the two triphenylphosphoranylideneacetate compounds, the fourth P-C(1) bond is shorter (1.762(6)-1.734(5) Å) than the three P-C(Ph) bonds (avg. 1.809(5) Å). The angles C(1)-P-C(Ph) are also larger (avg. 112.9(2)° for 6β and 111.9(2)° for 7α) than the C(Ph)-P-C(Ph) angles (avg. 105.8(2)° for 6 β and 106.9(2)° for 7α). These values suggest a multiple nature for the P-C(1) bond. In the nitro derivative, the nitro and the ester groups are disordered equally in positions 2 and 6. Key words: Wittig reactions, cyclic anhydrides, stabilized ylide, phosphoranylidenes, crystal structures.

SYNTHESIS OF ISOTOPICALLY LABELLED OLEFINS VIA THE WITTIG REACTION

1965 ◽  
Vol 43 (5) ◽  
pp. 1614-1624 ◽  
Author(s):  
J. G. Atkinson ◽  
M. H. Fisher ◽  
D. Horley ◽  
A. T. Morse ◽  
R. S. Stuart ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Dimethyl Sulfoxide ◽  
Wittig Reaction ◽  
Low Molecular Weight ◽  
Phosphonium Salts ◽  
Reaction Conditions ◽  
Selective Labelling ◽  
Wittig Reactions

A new application of the Wittig reaction to the preparation of olefins of low molecular weight which allows selective labelling in the vinyl or allyl positions with isotopes of hydrogen and carbon has been developed. Using the modification of the Wittig reaction introduced by E. J. Corey, in which a solution of the methylsulfinyl carbanion in dimethyl sulfoxide serves as the base, a series of olefins from C2 to C8 were synthesized. The synthesis was applied to the preparation of the following labelled compounds: 5-methylene-14C-bicyclo[2.2.1]hept-2-ene; propene-1-14C; 1-butene-1-14C; propene-1-d1; 2-methylpropene-1,1-d2; 2-methyl-d3-propene-3,3,3-d3; 2-methyl-2-butene-4,4,4-d3; 2-methyl-d3-2-butene-1,1,1-d3; methylene-d2-cyclohexane. For the synthesis of carbon-labelled olefins the reaction has few limitations since the intermediates and products are isotopically stable under the reaction conditions. Deuterium-labelled olefins can be obtained from deuterated formaldehyde or β-deuterated phosphonium salts, but α-deuteroketones and aldehydes and α-deuterophosphonium salts lose the isotope to the solvent.In all the Wittig reactions, benzene was formed as a by-product in 10–15% yield. The mechanism of benzene formation is probably analogous to that proposed by Seyferth involving the decomposition of a pentacovalent phosphorous intermediate.

scholarly journals Intramolecular Aza-Wittig Reaction of Iminophosphoranes with the b-Lactam Carbonyl Group

1997 ◽  
Author(s):  
Mateo Alajarín ◽  
Pedro Molina ◽  
Angel Vidai ◽  
Fulgencio Tovar
Keyword(s):  
Carbonyl Group ◽  
Wittig Reaction ◽  
Lactam Carbonyl Group ◽  
Lactam Carbonyl

The First Aza-Wittig Reaction of the β-Lactam Carbonyl Group

Synlett ◽  
1998 ◽  
Vol 1998 (11) ◽  
pp. 1288-1290 ◽  
Author(s):  
Mateo Alajarín
Keyword(s):  
Carbonyl Group ◽  
Wittig Reaction ◽  
Lactam Carbonyl Group ◽  
Lactam Carbonyl

An ab initio study of the p,π interaction: IV. Interaction of an ether oxygen atom with a carbonyl group

2006 ◽  
Vol 76 (6) ◽  
pp. 970-973 ◽  
Author(s):  
E. V. Feshina ◽  
V. P. Feshin
Keyword(s):  
Oxygen Atom ◽  
Ab Initio ◽  
Carbonyl Group ◽  
Ab Initio Study ◽  
Ether Oxygen Atom ◽  
Ether Oxygen
Sign in / Sign up

Export Citation Format

Share Document