The Origin of Diastereofacial Control in Allylboration Reactions Using Tartrate Ester Derived Allylboronates:  Attractive Interactions between the Lewis Acid Coordinated Aldehyde Carbonyl Group and an Ester Carbonyl Oxygen

2002 ◽  
Vol 124 (36) ◽  
pp. 10692-10697 ◽  
Author(s):  
Benjamin W. Gung ◽  
Xiaowen Xue ◽  
William R. Roush
Keyword(s):  
Carbonyl Group ◽  
Lewis Acid ◽  
Carbonyl Oxygen ◽  
Ester Carbonyl

INFRARED SPECTRA OF 2,6-DIMETHYL-4-PYRONE COMPLEXES

1961 ◽  
Vol 39 (6) ◽  
pp. 1184-1189 ◽  
Author(s):  
Denys Cook
Keyword(s):  
Complex Formation ◽  
Oxygen Atom ◽  
Carbonyl Group ◽  
Lewis Acid ◽  
Frequency Band ◽  
Infrared Spectra ◽  
Donor Site ◽  
Carbonyl Oxygen ◽  
Acid Strength ◽  
Group A

The infrared spectra of 2,6-dimethyl-4-pyrone in solution, and in complexes with HgCl2, ZnCl2, BF3, SbCl5, and HBr have been recorded. A band at 1639 cm−1 in the free pyrone moves to progressively lower frequencies in the complexes as the Lewis acid strength increases, identifying this band as the carbonyl stretching frequency and the donor site as the carbonyl group. A higher-frequency band, at 1678 cm−1 in the free pyrone, moves to lower frequency on complex formation, but to a much smaller extent, and is to be identified with a stretching mode of the ring. The site of protonation in 2,6-dimethyl-4-pyrone salts has been unequivocally shown to be the carbonyl oxygen atom.

cis-2,3-Di-tert-butylcyclopropanones

1997 ◽  
Vol 75 (7) ◽  
pp. 1030-1040 ◽  
Author(s):  
T.S. Sorensen ◽  
F. Sun
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Carbonyl Group ◽  
Trans Isomer ◽  
Carbonyl Oxygen ◽  
Highly Strained ◽  
Strained Alkenes ◽  
Acyclic Compound

The preparation of the strained cis-2,3-di-tert-butylcyclopropanone 2 from the acyclic compound, α,α′-dibromodineopentyl ketone 1, using a previously reported methodology, is dramatic evidence of both the existence of oxyallyl intermediates in the mechanism of this reaction, and of the integrity with which oxyallyls ring-close to cyclopropanones by a disrotatory route. Because of the bulky cis substituents, cyclopropanone 2 exhibits a number of unusual spectroscopic features (as compared to the trans isomer 5). With the aid of ab initio calculations on 2 and 5, it can be shown that the C2—C3 bond in 2 interacts with the carbonyl π-orbitals, thus causing the carbonyl oxygen to bend 12° out of the plane; this interaction is absent in 5 and the latter has a planar carbonyl group. As with other cyclopropanones, 2 can be photochemically decarbonylated. This process itself appears to be stereospecific even though highly strained alkenes are produced. Cyclopropanone 2 is thermally rearranged to the trans isomer 5 and the kinetics for this are reported; our favoured mechanism involves oxyallyl intermediates. Other reactions of 2 also appear to proceed through these oxyallyl species; for example, alcohols initially add to 2 to give α-alkoxy ends, solutions of 2 enter into very facile diene cycloadditions, and the dimerization of neat 2 also appears to involve these oxyallyl species. Keywords: cyclopropanones, oxyallyl, stereomutation, stereospecific decarbonylation, nonplanar carbonyl.

Oxiranes from methylenation of the ester carbonyl group by diazomethane

1988 ◽  
Vol 53 (14) ◽  
pp. 3321-3325 ◽  
Author(s):  
Paolo Strazzolini ◽  
Giancarlo Verardo ◽  
Angelo G. Giumanini
Keyword(s):  
Carbonyl Group ◽  
Ester Carbonyl ◽  
Ester Carbonyl Group

The mechanism of 1,3-dipolar cycloaddition reactions of cyclopropanes and nitrones — A theoretical study

2005 ◽  
Vol 83 (10) ◽  
pp. 1752-1767 ◽  
Author(s):  
D Wanapun ◽  
K A Van Gorp ◽  
N J Mosey ◽  
M A Kerr ◽  
T K Woo
Keyword(s):  
Lewis Acid ◽  
Density Functional ◽  
Cycloaddition Reaction ◽  
Acid Catalyst ◽  
Density Functional Theory Calculations ◽  
Reaction Rates ◽  
Carbonyl Oxygen ◽  
Dipolar Cycloaddition ◽  
Similar Reaction ◽  
Lewis Acid Catalyst

The 1,3-dipolar cycloaddition reaction of cyclopropanes and nitrones to give tetrahydro-1,2-oxazine has been studied with density functional theory calculations at the B3LYP/6-31+G(d,p) level of theory. Realistic substituents were modelled including those at the 2-, 3-, 4-, and 6-positions of the final oxazine ring product. The strained σ bond of the cyclopropane was found to play the role of an alkene in a conventional [3+2] dipolar cycloaddition. Two distinct, but similar, reaction mechanisms were found — an asymmetric concerted pathway and a stepwise zwitterionic pathway. The reaction barriers of the two pathways were nearly identical, differing by less than ~1 kcal/mol, no matter what the substituents were. The effect of a Lewis acid catalyst was examined and found to have a very large effect on the calculated barriers through coordination to the carbonyl oxygen atoms of the diester substituents on the cyclopropane. The reaction barrier was found to decrease by as much as ~19 kcal/mol when using a BF3 molecule as a model for the Lewis acid catalyst. Solvent effects and the nature of the regiospecificity of the reaction were also examined. Trends in the calculated barriers for the reaction were in good agreement with available trends in the reaction rates measured experimentally. Key words: 1,3-dipolar cycloaddition, cyclopropane, nitrone, tetrahydro-1,2-oxazines, ab initio quantum chemistry, mechanism.

Sign in / Sign up

Export Citation Format

Share Document