Synthesis, base strength, and prototropic behaviour of a number of alkyllumazines

1985 ◽  
Vol 63 (12) ◽  
pp. 3290-3293 ◽  
Author(s):  
Ross Stewart ◽  
S. J. Gumbley
Keyword(s):  
Sulfuric Acid ◽  
Isotopic Exchange ◽  
The Other ◽  
Methyl Groups ◽  
Hydrogen Atoms ◽  
Methyl Group ◽  
Neutral Compounds ◽  
Protonated Forms ◽  
Base Strength ◽  
Acid Catalyzed

A number of lumazines and 5-deazalumazines containing a methyl group at C-7 have been prepared, their pKBH+ values determined, and measurements made of the rates at which the hydrogen atoms of their 7-methyl groups undergo isotopic exchange in aqueous sulfuric acid. The presence of an alkyl group at N-8 in the protonated forms of these compounds activates the neighbouring methyl group at C-7; the effect is considerably larger than that previously observed for a methyl group at C-6, which is the other neighbouring position. The comparison of methyl and hydrogen at N-8 can be made only for the acid-catalyzed reaction because the structures of the neutral compounds, which take part in the base-catalyzed reaction, are not analogous.

Absolute stereochemistry of calopiptin

1968 ◽  
Vol 21 (8) ◽  
pp. 2095 ◽  
Author(s):  
JB Mc Alpine ◽  
NV Riggs ◽  
PG Gordon
Keyword(s):  
Mass Spectrometry ◽  
High Resolution ◽  
High Resolution Mass Spectrometry ◽  
The Other ◽  
Methyl Groups ◽  
Lower Field ◽  
Methyl Group ◽  
Low Field ◽  
Absolute Stereochemistry ◽  
Resolution Mass

The α,α?-diaryl-β,β-dimethyltetrahydrofurenoid lignan, calopiptin, from Piptocalyx moorei has been converted by demethylenation and methylation into veraguensin, now also isolated from Trimenia papuana (both species, family Trimeniaceae). Ozonolysis yields (-)-2,3-dimethylsuocinic acid which establishes the absolute trans configuration of the methyl groups. The benzylic proton giving a signal at low field from the other in the p.m.r, spectrum is assigned as trans to the adjacent methyl group by shielding and spin-decoupling arguments. The signal moves to even lower field on nitration of one of the aryl groups, identified as 3,4-dimethoxyphenyl by competitive nitration experiments and high-resolution mass spectrometry. Calopiptin is 2R-(3,4-dimethoxyphenyl)-3S,4S-dimethyl-5S-(3,4-methylenedioxyphenyl)tetrahydrofuran.

Kinetics of acid-catalyzed cyclization of substituted hydantoinamides to substituted hydantoins

1987 ◽  
Vol 52 (8) ◽  
pp. 1999-2004 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Gabriela Svobodová ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrogen Atom ◽  
Nitrogen Atom ◽  
Hydrochloric Acid ◽  
Dissociation Constants ◽  
Amide Group ◽  
The Other ◽  
Methyl Group ◽  
Acid Catalyzed ◽  
Cyclization Rate ◽  
Kinetics Of

The kinetics of acid-catalyzed cyclization of the hydantoinamides type R3-N(5)H-CO-N(3)R2-CH2-CO-N(1)HR1 (R1, R2, R3 = H and/or CH3) has been studied in 0·5 to 5 mol l-1 hydrochloric acid. The cyclization rate is limited by the rate of the attack of nitrogen atom N(5) on the carbon atom of the protonated amide group. The dissociation constants of the protonated hydantoinamides and rate constants of their cyclizations have been determined. Replacement of hydrogen atom by methyl group at the N(5) nitrogen atom accelerates the cyclization about two times., the same substitution at N(3) accelerates about 50x, whereas at N(1) it results in a 300 fold retardation. With the hydantoinamides having R3 = CH3, the cyclization rate of the protonated hydantoinamide increases with increasing concentration of hydrochloric acid, whereas with the other derivatives this value is independent of the acid concentration.

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.

THE WALLACH REARRANGEMENT: PART II. KINETICS AND MECHANISM OF THE ACID-CATALYZED REARRANGEMENT OF AZOXYBENZENE

1965 ◽  
Vol 43 (4) ◽  
pp. 862-875 ◽  
Author(s):  
E. Buncel ◽  
B. T. Lawton
Keyword(s):  
Sulfuric Acid ◽  
Proton Transfer ◽  
Acid Concentration ◽  
Entire Range ◽  
Kinetics And Mechanism ◽  
The Other ◽  
Rate Data ◽  
Spectrophotometric Methods ◽  
Aqueous Sulfuric Acid ◽  
Acid Catalyzed

The rate of rearrangement of azoxybenzene to p-hydroxyazobenzene has been measured in 75.3–96.4% sulfuric acid at 25° and in 65.0–90.4% sulfuric acid at 75.5° by spectrophotometric methods. The pKa of azoxybenzene in aqueous sulfuric acid has also been determined. It is found that although azoxybesssnzene is almost completely protonated over the entire range of acid concentration studied, the rate increases by more than 1 000-fold. A two-proton process is therefore indicated and mechanisms are proposed involving a dication (II) as the key intermediate. The rate data do not allow differentiation between two proposed mechanisms, one involving two equilibrium protonations, and the other a single equilibrium protonation followed by rate-determining proton transfer. Past mechanisms of the Wallach rearrangement are discussed.

Ambident nucleophiles. III. N-bonded vs. C-bonded adduct formation on reaction of imidazolide anions with 1,3,5-trinitrobenzene

1985 ◽  
Vol 63 (4) ◽  
pp. 866-870 ◽  
Author(s):  
M. P. Simonnin ◽  
J. C. Halle ◽  
F. Terrier ◽  
M. J. Pouet
Keyword(s):  
Proximity Effect ◽  
Adduct Formation ◽  
The Other ◽  
Methyl Groups ◽  
Kinetic Control ◽  
Methyl Group ◽  
Low Field ◽  
Substitution Site ◽  
Field Shift ◽  
Subsequent Conversion

Imidazolide anions of imidazole, 2- and 4-methylimidazoles, 4,5-dimethyl and 4,5-diphenylimidazoles react with 1,3,5-trinitrobenzene (TNB) in dimethylsulfoxide (DMSO) to yield, initially, N-bonded σ-adducts under kinetic control. These undergo a subsequent conversion to C-adducts, which are the thermodynamically stable products. The formation of N,C-diadducts from the reversible attack of a second TNB molecule on the imidazolide moiety of the C-adducts is also observed. Provided that the corresponding position of the parent imidazolide anion is free, the formation of C-adducts occurs preferentially at the C-4 or C-5 carbon atom. However, C-2 substitution is observed in 4,5-disubstituted derivatives. Structures and preferred conformations of some adducts and diadducts are deduced from nOe experiments. The mechanisms of the various reactions are discussed. Evidence is presented that adduct formation results in a low-field shift of methyl groups located in a position adjacent to the substitution site, while all the other protons move upfield. This unusual deshielding presumably reflects a proximity effect between a methyl group and the hydrogen atom attached to the sp3 carbon of the adducts.

Steric activation in prototropic reactions of pyrazine derivatives. II. The Brønsted relation

1986 ◽  
Vol 64 (6) ◽  
pp. 1090-1092 ◽  
Author(s):  
K. Nagarajan ◽  
T. W. S. Lee ◽  
R. R. Perkins ◽  
Ross Stewart
Keyword(s):  
Transition State ◽  
The Other ◽  
Steric Effects ◽  
Methyl Groups ◽  
Reaction Centre ◽  
Organic Electrolytes ◽  
Methyl Group ◽  
Pyridine Bases ◽  
Tentative Explanation ◽  
High Concentrations

The rate of deprotonation of the 2-methyl group in 1,2,3-trimethylpyrazinium ion by carboxylate, aniline, and pyridine bases has been measured in D2O. Carboxylate ions containing bulky groups near the reaction centre, e.g. ortho benzoates, react faster than predicted by the Brønsted equation that correlates the reactions of unhindered carboxylates. Anilines and pyridines, on the other hand, show conventional steric effects. A tentative explanation for the activation engendered by groups adjacent to the carboxylate centre is based on the known effect that high concentrations of organic electrolytes have on the strengths of carboxylic acids but not of amines. Since ortho carboxylate ions have their relative basicities increased by an alkyl-rich environment, it is argued that the reactive methyl groups of the substrate might provide such an interaction in the transition state.

Fate of the Methyl Group in the Sulfuric Acid Catalyzed Oxidation of Toluene to Phenol

1980 ◽  
Vol 19 (3) ◽  
pp. 468-470 ◽  
Author(s):  
James E. Lyons ◽  
George Suld ◽  
Robert W. Shinn ◽  
Chao-Yang Hsu
Keyword(s):  
Sulfuric Acid ◽  
Methyl Group ◽  
Acid Catalyzed ◽  
Catalyzed Oxidation

A facile and general acid-catalyzed deuteration at methyl groups of N-heteroarylmethanes

2017 ◽  
Vol 15 (12) ◽  
pp. 2507-2511 ◽  
Author(s):  
Min Liu ◽  
Xue Chen ◽  
Tieqiao Chen ◽  
Shuang-Feng Yin
Keyword(s):  
Large Scale ◽  
Methyl Groups ◽  
Methyl Group ◽  
General Acid ◽  
Good Potential ◽  
Acid Catalyzed ◽  
Large Scale Synthesis

A general acid-catalyzed deuteration at the methyl group of N-heteroarylmethanes was achieved, which could be conducted at a 500 mmol-scale, showing its good potential for use in large-scale synthesis.

Temperature dependence of the crystal structure of 3,5-di-tert-butylpyrazole from 10 K

2004 ◽  
Vol 60 (5) ◽  
pp. 621-625 ◽  
Author(s):  
Alexandre N. Sobolev ◽  
Allan H. White
Keyword(s):  
Pyrazole Ring ◽  
The Other ◽  
Methyl Groups ◽  
Asymmetric Unit ◽  
Temperature Dependent ◽  
Methyl Group ◽  
Butyl Group ◽  
Structure Determinations ◽  
History Of ◽  
The Subject

A single crystal of 3,5-di-tert-butylpyrazole has been the subject of structure determinations at 10, 100, 120 and 299 K. Above ∼ 110 K, the structure is Pbca, a ≃ 11.3, b ≃ 20.6, c ≃ 10 Å, Z = 8. Below 110 K, the c axis is doubled and the space group becomes Pb21 a, Z = 16. Here the asymmetric unit is comprised of four molecules, arranged as a pair of overlapping hydrogen-bonded dimers, all components being ordered. In each case one methyl group of each t-butyl group lies coplanar with its parent pyrazole ring and, within each quasi-inversion-related dimer, one molecule has both of these methyl groups directed away from the N2 component `cis', while in the other, one methyl group is toward (`trans'). Above 110 K the four molecules collapse into one, with one t-butyl group (corresponding to an overlaid `cis/trans' pair of the low-temperature form) modelled as disordered. The disorder has been previously described as `temperature dependent' (Deacon et al., 2001), but the present studies suggest it to be dependent on the history of the particular specimen as well.

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