Stereoselectivity of C(3) methylation and aldol condensation of camphor and derivatives

1991 ◽  
Vol 69 (3) ◽  
pp. 558-566 ◽  
Author(s):  
J. H. Hutchinson ◽  
D. L. F. Li ◽  
T. Money ◽  
M. Palme ◽  
M. R. Agharahimi ◽  
...  
Keyword(s):  
Key Words ◽  
Aldol Condensation ◽  
Hydrogen Atoms ◽  
Methyl Group

The stereoselectivity of methylation and aldol condensation of camphor and derivatives is determined by the presence or absence of a C(7) syn-methyl group and (or) C(5) and C(6) endo-hydrogen atoms. Key words: camphor, C(3) methylation, C(3) aldol.

Remarkable kinetic stability of α-thiocarbamoyl substituted 4-methoxybenzylcations

1998 ◽  
Vol 76 (12) ◽  
pp. 1910-1915 ◽  
Author(s):  
Robert A McClelland ◽  
Victoria E Licence ◽  
John P Richard ◽  
Kathleen B Williams ◽  
Shrong-Shi Lin
Keyword(s):  
Key Words ◽  
Strong Interaction ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Visible Absorption ◽  
Methyl Group ◽  
Thioamide Group ◽  
Azide Ion ◽  
Uv Visible ◽  
Leaving Groups

4-Methoxybenzyl cations bearing α-(N,N-dimethylcarbamoyl) and α-(N,N-dimethylthiocarbamoyl) substituents have been generated photochemically upon irradiation of precursors with pentafluorobenzoate or 4-methoxybenzoate leaving groups. The ions have been observed with flash photolysis in 40:60 acetonitrile:water and in 50:50 methanol:water, and rate constants were measured for their decay in solvent alone and for their capture by azide ion. The cations so studied and their lifetimes in 40% acetonitrile are 6, ArC+H-CONMe2, 0.6 μs; 2, ArC+H-CSNMe2, 7 ms; and 4, ArC+(CH3)-CSMe2, 6 ms, where Ar = 4-MeOC6H4. The cation 4 reacts with solvent by elimination of a proton from the α-methyl group, and the rate constant for solvent addition must be less than 1 s-1. The CSNMe2 substituted cations are 105-107-fold longer lived than analogs where the thioamide group has been replaced with an α-methyl. The UV-visible absorption spectra of these two cations also show significant differences from those of typical 4-methoxybenzyl cations. Thus, both the lifetimes and spectra point to a strong interaction of the benzylic centre with the thioamide group. Key words: flash photolysis, thiocarbamoyl stabilized carbocation, photosolvolysis.

Reactions of free radicals with aromatic compounds in the gaseous phase. I. Kinetics of the reaction of methyl radicals with toluene

1964 ◽  
Vol 17 (12) ◽  
pp. 1329 ◽  
Author(s):  
MFR Mulcahy ◽  
DJ Williams ◽  
JR Wilmshurst
Keyword(s):  
Flow System ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Methyl Group ◽  
Benzyl Radical ◽  
Toluene Molecule ◽  
Benzyl Radicals ◽  
Butyl Peroxide ◽  
Kinetics Of

The kinetics of abstraction of hydrogen atoms from the methyl group of the toluene molecule by methyl radicals at 430-540�K have been determined. The methyl radicals were produced by pyrolysis of di-t-butyl peroxide in a stirred-flow system. The kinetics ,agree substantially with those obtained by previous authors using photolytic methods for generating the methyl radicals. At toluene and methyl-radical concentrations of about 5 x 10-7 and 10-11 mole cm-3 respectively the benzyl radicals resulting from the abstraction disappear almost entirely by combination with methyl radicals at the methylenic position. In this respect the benzyl radical behaves differently from the iso-electronic phenoxy radical, which previous work has shown to combine with a methyl radical mainly at ring positions. The investigation illustrates the application of stirred-flow technique to the study of the kinetics of free-radical reactions.

Studies on the thermal coking of bitumen. I. The use of pyrene-d10 as a probe for evaluating the extent of hydrogen shuttling reaction

1991 ◽  
Vol 69 (1) ◽  
pp. 116-120 ◽  
Author(s):  
M. J. Kirk ◽  
T. S. Sorensen
Keyword(s):  
Free Radicals ◽  
Key Words ◽  
Hydrogen Exchange ◽  
Solvent Free ◽  
Hydrogen Donor ◽  
Organic Reactions ◽  
Hydrogen Atoms ◽  
Donor Solvent ◽  
Key Words Bitumen

The organic reactions that take place during the thermal coking of bitumen are extremely complex and deep-seated, but obviously hydrogen atoms originally attached to carbons that form coke will have moved to a new carbon site (net addition of hydrogen, resulting in upgraded bitumen). Accompanying this process, one expects some general hydrogen shuttling between non-coking molecules. This paper describes an approach to determing the extent of this latter process by the addition of a small amount of perdeuterated pyrene to the bitumen prior to the coking operation. The in situ pyrene functions as in indicator, allowing one to establish the extent and other mechanistic details of the "hydrogen donor" reactions that take place during coking. There is no indication that the pyrene substantially modifies the normal course of the reaction, hence the analogy to an indicator. Key words: bitumen coking, pyrene, hydrogen exchange, donor solvent, free radicals.

scholarly journals The mechanism of glucose 6-phosphate–d-myo-inositol 1-phosphate cyclase of rat testis. The involvement of hydrogen atoms

1968 ◽  
Vol 108 (1) ◽  
pp. 125-129 ◽  
Author(s):  
J. E. G. Barnett ◽  
D. L. Corina
Keyword(s):  
Hydrogen Atom ◽  
Isotope Effect ◽  
Ternary Complex ◽  
Aldol Condensation ◽  
Hydrogen Atoms ◽  
Original Activity ◽  
Rat Testis ◽  
Inositol 1 ◽  
Apparent Loss

Comparison of the initial 3H/14C ratios in specifically labelled d-glucose 6-phosphates with the final ratios in myo-inositol produced by glucose 6-phosphate–d-myo-inositol 1-phosphate cyclase from rat testis showed that, during the conversion, the hydrogen atoms at C-1 and C-3 were fully retained, one hydrogen atom was lost from C-6, and that at C-5 was apparently retained to the extent of 80–90%. The loss of 3H could not be stimulated by addition of unlabelled NADH, and when unlabelled substrate was used 3H from [3H]NADH and [3H]water was not incorporated. Treatment of the enzyme with charcoal abolished the activity, and this was restored to 25–50% of the original activity by NAD+. The charcoal-treated enzyme again apparently gave 85% retention of hydrogen with [5−3H]glucose 6-phosphate as substrate in the presence of NAD+ alone, but the retention was decreased to 65% with excess of NADH. The results are interpreted as indicating that the cyclization proceeds by an aldol condensation in which C-5 is oxidized by NAD+ in a tightly-bound ternary complex, and that the apparent loss of 3H when untreated enzyme is used is due to an isotope effect. It is suggested that after treatment with charcoal some exchange of NADH with an external pool may take place.

The effect of the position of the methyl group on the helical twisting powers of aldol condensation products of methyl cyclohexanones

2002 ◽  
Vol 29 (7) ◽  
pp. 995-1000 ◽  
Author(s):  
J. Lub ◽  
W. Ten Hoeve ◽  
W. P. M. Nijssen ◽  
L. Diaz ◽  
R. T. Wegh
Keyword(s):  
Aldol Condensation ◽  
Methyl Group ◽  
Condensation Products

scholarly journals Synthesis of Some Biologically Important 3-Oxacepham Derivatives

1970 ◽  
Vol 5 (1) ◽  
pp. 47-51 ◽  
Author(s):  
Mohammad Rafiqul Islam ◽  
Mohammad Nurnabi ◽  
AM Sarwaruddin Chowdhury ◽  
Mohammad Mehdi Masud
Keyword(s):  
Key Words ◽  
Full Text ◽  
Crystallographic Analysis ◽  
High Yield ◽  
Methyl Group ◽  
X Ray ◽  
Tert Butyl ◽  
Relative Stereochemistry

The 6H-oxathiazines 1a-e having imine moiety underwent [2+2] cycloaddition with phenoxyacetylchloride in the presence of Et3N to give β-lactam derivatives 2a-e in high yield. The X-ray crystallographic analysis revealed the relative stereochemistry that the substituents at C-2 and C-4 were cis configurated. The subtituents at C-6 and C-7 were also cis to each other. However, the 6H-oxathiazines 1f-i containing tert-butyl or methyl group at C-4 did not undergo the cycloaddition. Key words: Azetedinone, β-lactam, oxacepham, cycloaddition, imine, ketene, oxathiazine. Dhaka Univ. J. Pharm. Sci. Vol.5(1-2) 2006 The full text is of this article is available at the Dhaka Univ. J. Pharm. Sci. website

Photooxidation of methyl ethyl ketone vapor

1967 ◽  
Vol 45 (22) ◽  
pp. 2741-2748 ◽  
Author(s):  
D. E. Hoare ◽  
D. A. Whytock
Keyword(s):  
Methyl Ethyl Ketone ◽  
Relative Rate ◽  
Quantum Yields ◽  
Methyl Ethyl ◽  
Hydrogen Atoms ◽  
Methyl Group ◽  
Ethyl Group ◽  
Relative Rate Constants ◽  
The Individual ◽  
Time Extrapolation

The photochemical reaction between methyl ethyl ketone and oxygen has been studied at 150 °C with light of 3 130 Å. Measurement of the quantum yields of the major products of the reaction indicates the chain nature of the reaction, the length of the chain decreasing with increase in time. Extrapolation of quantum yields of products to zero time allows the evaluation of several relative rate constants and at least an indication of the individual radical sources of the observed products. It is shown that abstraction of hydrogen atoms from the methyl group takes place at least at a quarter the rate of abstraction of a secondary hydrogen from the ethyl group at 150 °C. In the initial products the ethyl group gives mainly acetaldehyde or perpropionic acid, the methyl group gives formaldehyde and methanol, and the carbonyl group gives carbon dioxide and perpropionic acid with a little carbon monoxide.

scholarly journals Incorporation of 5-methylorcylaldehyde and methionine into the acetogenin (polyketide) gliorosein in Gliocladium roseum I.M.I. 93065

1968 ◽  
Vol 109 (1) ◽  
pp. 1-11 ◽  
Author(s):  
M. W. Steward ◽  
N. M. Packter
Keyword(s):  
Aromatic Compound ◽  
Methyl Groups ◽  
Gliocladium Roseum ◽  
Hydrogen Atoms ◽  
Group 14 ◽  
Methyl Group ◽  
Appreciable Difference ◽  
Specific Activities

1. methyl−14C-labelled 1,3-dihydroxy-4,5-dimethylbenzene, 5-methylorcylaldehyde and 5-methylorsellinic acid were synthesized from orcinol and sodium [14C]cyanide and tested for activity as precursors of gliorosein. ring−14C-labelled orcylaldehyde was also prepared. 5[14C]-Methylorcylaldehyde was incorporated into gliorosein (36% conversion); all the radioactivity was located in the C-methyl groups. 5-Methylorsellinic acid was decarboxylated by Gliocladium roseum and the resulting phenol was secreted into the medium. 2. The formation of an enzyme-bound derivative of 5-methylorsellinic acid as the first aromatic compound in the biosynthesis of gliorosein is suggested to explain these results. 3. ring−14C-labelled 3,4-dihydroxy-6-methyltoluquinone was also effectively incorporated into gliorosein and related products (20% conversion). 4. Sodium [14C]formate and [Me−14C]-methionine were incorporated into gliorosein and related products (15·4 and 22·2% conversion respectively). Isolation and estimation of the radioactivity in the O-methyl and C-methyl groups in the 14C-labelled gliorosein thus formed showed an appreciable difference in the specific activities of the two types of methyl group (14 and 15% respectively). The results in the doubly-labelled methionine experiment indicate that the C-methyl group arises in the same manner as that in ergosterol; one of the original hydrogen atoms of the methyl group is lost. This confirms that C-methylation occurs at an ethylenic group at the aliphatic level. 5. The sequence of reactions at the aromatic level leading to the formation of gliorosein is proposed as 5-methylorsellinyl-enzyme→3-hydroxy-5-methylorsellinyl-enzyme→3,4-dihydroxy-6-methyltoluquinol→3,4-dimethoxy-6-methyltoluquinol→gliorosein.

La photochimie du cis-penta-1,3-diène, en phase gazeuse à 184,9 et 147,0 nm

1991 ◽  
Vol 69 (8) ◽  
pp. 1245-1251
Author(s):  
Guy J. Collin ◽  
Hélène Deslauriers ◽  
George R. De Maré
Keyword(s):  
Key Words ◽  
Energy Content ◽  
Phase Gazeuse ◽  
Radical Scavenger ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Lower Yield ◽  
Uv Photolysis ◽  
Vacuum Uv

We have studied the 184.9 and 147.0 nm photochemistry of gaseous cw-1,3-pentadiene: the main products observed at 184.9 nm are trans-1,3-pentadiene and 1,3-cyclopentadiene. The formation of radicals also occurs as shown through the use of DI as a radical scavenger. Cyclopentadiene is the likely product of successive eliminations of two hydrogen atoms from the photoexcited molecule after rearrangement of the pentadienyl radical to the cyclopentenyl structure: Ф0(cyclo-C5H6) ≈ 0.25. Elimination of a methyl radical (Ф0 ≈ 0.50) also occurs, with formation of CH2=CHCH=ĊH* and, in a lower yield, CH2=C=CHĊH2*. However, it is not possible to identify properly the mechanism of the formation of the latter radical. It may be the result of the isomerization of either the first photoexcited molecule or the excited 1,3-butadienyl radicals. A small amount of 1,4-pentadiene formation is also observed (Ф0 ≈ 0.035 ± 0.015). At 147.0 nm, the same characteristics are observed, together with higher fragmentation due to the higher energy content of the photoexcited molecules. It appears that the photofragmentation at both wavelengths is more in line with that of acyclic alkenes than with that of 1,3-butadiene, which tends to undergo isomerization of the photoexcited molecules to the 1,2-butadiene structure. Key words: 1,3-pentadiene, far UV, vacuum UV, photolysis, monomolecular, fragmentation, stabilization.

Sense of sequential 1,5-sigmatropic rearrangements of dimethyl-3,3-dialkyl-3H-pyrazole-4,5-dicarboxylates. Crystal and molecular structures of two dimethyl-4,5-dialkyl-1H-pyrazole-1,3-dicarboxylates

1991 ◽  
Vol 69 (3) ◽  
pp. 373-378 ◽  
Author(s):  
Christopher S. Frampton ◽  
Michael W. Majchrzak ◽  
John Warkentin
Keyword(s):  
Dicarboxylic Acid ◽  
Key Words ◽  
Dimethyl Ester ◽  
Molecular Structures ◽  
X Ray Diffraction ◽  
Methyl Group ◽  
X Ray ◽  
Crystal And Molecular Structures ◽  
Sigmatropic Rearrangements ◽  
Methoxycarbonyl Group

3,3-Dialkyl-3H-pyrazole-4,5-dicarboxylic acid dimethyl esters (4), obtained by cycloaddition of R1R2C=N+=N− (R1 = R2 = CH3; R1 = CH3, R2 = CH2CH3) to CH3O2CC≡CCO2CH3, rearrange thermally by 1,5-sigmatropic alkyl shifts to both N and C. The latter rearrangement is followed by two successive 1,5-sigmatropic shifts of a methoxycarbonyl group. Final products of the threefold rearrangement were shown to be 4,5-dialkyl-1H-pyrazole-1,3-dicarboxylic acid dimethyl esters (6), rather than the isomeric 3,4-dialkyl-1H-pyrazole-1,5-dicarboxylic acid dimethyl esters (7), by means of single crystal X-ray diffraction. Those products therefore result from alkyl migration to C-4 of 4, followed by sequential migration of the methoxycarbonyl group, initially at C-4, to C-3 and then to N-2 of 4. In the initial alkyl migration step, ethyl migrates in preference to methyl, and in subsequent migration steps the methoxycarbonyl group migrates faster than the ethyl or methyl group. Crystals of 4-ethyl-5-methyl-1H-pyrazole-1,3-dicarboxylic acid dimethyl ester (6b) are monoclinic, of space group P21/n, with a = 7.907(1) Å, b = 11.087(2) Å, c = 13.199(3) Å, V = 1124.9(4) Å 3, Dc = 1.34 g cm−3, Dm = 1.33 g cm−3 for Z = 4, and R1 = 0.0772 (R2 = 0.0626) for 1474 reflections (R1 = 0.0428, R2 = 0.0422 for 903 reflections with I > 3σ(I)). The structure of 6a is similar. Key words: 3,3-dialkyl-3H-pyrazoles, 1,5-sigmatropic rearrangements of; 4,5-dialkyl-1H-pyrazoles, crystal and molecular structures; 1,5-sigmatropic rearrangements of pyrazoles, sense of.

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