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.

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.

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.

Mechanism of Wittig reaction with cyclic anhydrides

1992 ◽  
Vol 70 (7) ◽  
pp. 1985-1996 ◽  
Author(s):  
Margaret M. Kayser ◽  
Krista L. Hatt ◽  
Donald L. Hooper
Keyword(s):  
Wittig Reaction ◽  
Reaction Pathway ◽  
Spectroscopic Methods ◽  
Cyclic Anhydrides

The reactions of stabilized phosphoranes with cyclic anhydrides give enol-lactones as final products. The initial condensation, however, leads to the formation of acyclic adducts that are observable by NMR, can be easily trapped, and, in some cases, can be isolated. A study of the mechanism of these condensations by NMR spectroscopic methods and by various trapping experiments is described and the reaction pathway is proposed.

Effects of Base π-Stacking on Damage to DNA by Low-Energy Electrons

2004 ◽  
Vol 108 (51) ◽  
pp. 11381-11387 ◽  
Author(s):  
Iwona Anusiewicz ◽  
Joanna Berdys ◽  
Monika Sobczyk ◽  
Piotr Skurski ◽  
Jack Simons
Keyword(s):  
Low Energy ◽  
Π Stacking ◽  
Low Energy Electrons

Quantitative Assessment of Force Fields on Both Low-Energy Conformational Basins and Transition-State Regions of the (ϕ−ψ) Space

2010 ◽  
Vol 7 (2) ◽  
pp. 402-419 ◽  
Author(s):  
Zhiwei Liu ◽  
Bernd Ensing ◽  
Preston B. Moore
Keyword(s):  
Transition State ◽  
Quantitative Assessment ◽  
Force Fields ◽  
Low Energy

scholarly journals Photochemical approach to functionalized benzobicyclo[3.2.1]octene structures via fused oxazoline derivatives from 4- and 5-(o-vinylstyryl)oxazoles

2014 ◽  
Vol 10 ◽  
pp. 2222-2229 ◽  
Author(s):  
Ivana Šagud ◽  
Simona Božić ◽  
Željko Marinić ◽  
Marija Šindler-Kulyk
Keyword(s):  
Silica Gel ◽  
Ring Opening ◽  
Spectroscopic Methods ◽  
Intramolecular Cycloaddition ◽  
Wittig Reactions ◽  
Van Leusen Reaction ◽  
Oxazoline Derivatives

Novel cis/trans-4- and cis/trans-5-(2-vinylstyryl)oxazoles have been synthesized by Wittig reactions from the diphosphonium salt of α,α’-o-xylene dibromide, formaldehyde and 4- and 5-oxazolecarbaldehydes, respectively. In contrast, trans-5-(2-vinylstyryl)oxazole has been synthesized by the van Leusen reaction from trans-3-(2-vinylphenyl)acrylaldehyde which is prepared from o-vinylbenzaldehyde and (formylmethylene)triphenylphosphorane. The 4- and 5-(2-vinylstyryl)oxazoles afford, by photochemical intramolecular cycloaddition, diverse fused oxazoline-benzobicyclo[3.2.1]octadienes, which are identified and characterized by spectroscopic methods. The photoproducts formed are relatively unstable and spontaneously or on silica gel undergo oxazoline ring opening followed by formation of formiato- or formamido-benzobicyclo[3.2.1]octenone derivatives. On irradiation of 4-(2-vinylstyryl)oxazole small quantities of electrocyclization product, 4-(1,2-dihydronaphthalen-2-yl)oxazole, are isolated and spectroscopically characterized.

Regioselectivity of metal hydride reductions of unsymmetrically substituted cyclic anhydrides. systems where "steric hindrance along the preferred reaction path" rationalization is not applicable

1980 ◽  
Vol 58 (23) ◽  
pp. 2484-2490 ◽  
Author(s):  
Margaret M. Kayser ◽  
Peter Morand
Keyword(s):  
Transition State ◽  
Metal Hydride ◽  
Reaction Path ◽  
Steric Effects ◽  
Carbonyl Groups ◽  
Qualitative Interpretation ◽  
Alkaline Cation ◽  
Cyclic Anhydrides ◽  
Late Transition ◽  
Carbonyl Function

Metal hydride reductions of planar cyclic anhydrides such as methylmaleic or 3-substituted phthalic anhydrides occur preferentially at the sterically more hindered carbonyl function. This regioselectivity cannot be rationalized in terms of "the most favourable pathway for non-perpendicular attack by a nucleophile" since both carbonyl groups present are equally accessible to non-perpendicular approach. A study which takes into account the alkaline cation and inductive, mesomeric, and steric effects has been conducted for the reduction of several conjugated and aromatic anhydrides. A qualitative interprétation for the regioselectivities observed in these reductions (as well as in reductions already reported in the literature) is suggested. An early transition state for the catalyzed versus late transition state for the non-catalyzed process is proposed.

Two Variations of Solvent-Reduced Wittig Olefination Reactions — Comparison of Solventless Wittig Reactions to Wittig Reactions under Ultrasonication with Minimal Work-Up.

ChemInform ◽  
2005 ◽  
Vol 36 (50) ◽  
Author(s):  
Masataka Watanabe ◽  
Goreti Ribeiro Morais ◽  
Shuntaro Mataka ◽  
Keiko Ideta ◽  
Thies Thiemann
Keyword(s):  
Wittig Olefination ◽  
Wittig Reactions ◽  
Minimal Work ◽  
Work Up ◽  
Olefination Reactions

The reactions of simple dimethylallylamines with dimethyl acetylenedicarboxylate. Formation of 1-dimethylamino-2-allylmaleates via formal allyl transfer

1988 ◽  
Vol 66 (7) ◽  
pp. 1686-1694 ◽  
Author(s):  
Adrian L. Schwan ◽  
John Warkentin
Keyword(s):  
Proton Transfer ◽  
Transition State ◽  
Carbonyl Group ◽  
Quaternary Ammonium ◽  
Methyl Groups ◽  
Dimethyl Acetylenedicarboxylate ◽  
Tertiary Amines ◽  
Reversible Formation ◽  
Zwitterionic Intermediate ◽  
Membered Transition State

Tertiary amines bearing two methyl groups and an allylic substituent (X) react with dimethyl acetylenedicarboxylate (DMAD) to afford the corresponding 1-dimethylamino-2-X′ maleates, in which X′ is the allylic isomer of X. The mechanism postulated involves reversible formation of a zwitterion by attack of the amine at an sp-carbon of DMAD. The zwitterion then undergoes intramolecular allyl transfer, through a 6-membered transition state. Evidence for a zwitterionic intermediate (quaternary ammonium allenolate) includes capture of the allenolate centre by intramolecular addition to a carbonyl group and by proton transfer from chloroform.

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