Cleavage methylation

Acid hydrolysis of hamameli-tannin readily causes liberation of the carbohydrate component, 2-(hydroxymethyl)-D-ribose, together with two molar proportions of gallic acid, which presumably occupy similar positions, since there is no difference in their rate of cleavage. Methylation of hamameli-tannin with diazomethane, and subsequent alkaline hydrolysis,... 

SCHEME 5. Richardson s application of the Fischer nitromethane cyclization to the sugar dialdehyde derived from periodate cleavage methyl a-L-rhamnopyranoside (1961). 

Peptide Protein Phase Resin Cleavage Methyl Cleavage Ref... 

Peptide Protein Coupling Resin Resin Cleavage +Methyl Oeavage Ref... 

In coumarins which bear large alkyl side chains, such as osthol (122), the primary fragmentation does not involve carbon monoxide loss. The dominant processes are side chain cleavage, methyl radical elimination from the side chain, and loss of a methoxyl radical. The mass spectra of this and related naturally occurring coumarins have been intensively studied and reviewed (75RCR603). 

A moderate to strong peak at mlz 61 is present (see alkyl sulfide cleavage, Figure 1.28) in the spectrum of all except tertiary sulfides. When an a-methyl substituent is present, mlz 61 is the ion, CH3CH=SH+, resulting from the double cleavage. Methyl primary sulfides cleave at the a, (3-bond to give the mlz 61 ion, CH3—S+=CH2... 

Figure 9. Identification of metabolites A through D in urine of rats treated with CDA led to the proposed hidden metabolites shown here in brackets. The reactive sulfate conjugate apparently undergoes glutathione conjugation, further metabolism via the mercapturic acid pathway and, finally, C-S cleavage, methylation and sulfur oxidation of C to yield D.

Wasserman and Saito have used diphenyl sulfide to intercept dioxetanes formed in the sensitized photooxidations of certain unsaturated systems. Thus reaction of cw-dimethoxystilbene (1) with singlet oxygen yields only the diox-etane (2) and the product of cleavage, methyl benzoate. However, addition of diphenyl sulfide to the reaction results in formation of benzil dimethyl ketal... 

Supported catalysts involving palladium on carbon and dendrimer-encapsulated palladium and a polymer-supported phosphine palladium catalyst have facilitated C-C coupling reactions in SCCO2. Polymer-tethered substrates or amine bases have also been successfully used for the Mizoroki-Heck and Suzuki-Miyaura reactions in SCCO2. For example, REM resin underwent a Mizoroki-Heck reaction with iodobenzene to yield, after cleavage, ( )-methyl cinnamate 48 (74%) (Scheme 88). It is assumed that SCCO2 acts as a good solvent that swells the polymers and exposes reactive sites. 

The results of selective cleavage, methylation, and oxidation with chromic oxide have shown that the repeating unit of the polysaccharide chain of the lipopolysaccharide from Sh. dysenteriae is 2-acetamido-2-deoxy-j3-D-galactosyl-(1 -> 3)-a-D-galactopyranosyl-(l 6)-o -D-glucopyranose, to which is attached... 

The most common stereoselective syntheses involve the formation and cleavage of cyclopentane and cyclohexane derivatives or their unsaturated analogues. The target molecule (aff-cts)-2-methyl-l,4-cyclohexanediol has all of its substituents on the same side of the ring. Such a compound can be obtained by catalytic hydrogenation of a planar cyclic precursor. Methyl-l,4-benzoquinone is an ideal choice (p-toluquinone M. Nakazaki, 1966). 

Finally the chemical aromatization of Ring A which occurs in nature in the biosynthesis of estrogens must be mentioned. It can be done by thermal cleavage of the C-19 methyl group in 1,4-dien-3-ones (H.H. Inhoffen, 1940 C. Djerassi, 1950) and was later achieved at lower temperatures with lithium — biphenyl in THF (H.L. Dryden, Jr., 1964). 

Oxidative cleavage of the complex 549 with CuCri affords 2,3-bis(chloro-methyl)-1,3-butadiene (550) and regenerates PdCri. Thus the preparation of this interesting dimerization product 550 can be carried out with a catalytic amount of PdCl2 and two equivalents of CuCb in MeCN[495], Similarly, treatment of allene with PdBr2 affords the dimeric complex 551. Treatment of this complex with 2 equiv, of bromine yields the dibromide 552. The tetra-bromide 553 is obtained by the reaction of an excess of bromine[496]. Similarly,... 

Amino-4-phenylthiazole when heated with Raney Ni is reported to yield acetophenone (469). In the course of a general study on reductive cleavage in heterocyclic systems Hoff et al. studied the reaction of 2-amino-4-methylthiazole with Na in liquid ammonia. Two equivalents of Na are necessary to obtain a mixture of 4-methyl-3-thiazoline (240) and... 

The thiazolium is not acidic enough for observing directly solvation of the molecule (or an hydrolysis and subsequent cleavage of the ring) (24) without adding a base, as it is the case for benzoxazolium or benzothiazolium. With the same dilution (10 mole liter ), it is necessary to add sodium ethylate to the solution of 2-methyl-4.5-diphenylthiazolium to observe the equilibrium described above. A new band appears in the UV spectrum at 320 nm that is attributed to the ethoxy derivative by analogy to what has been observed with other benzothiazoliums (26),... 

Methyl free radicals, generated either by thermolysis of lead tetracetate in acetic acid solution (401) or by radical cleavage of dimethylsulfoxide by H2O2 and iron (II) salts (408), afford 2- and 5-methylthiazole in the proportion of 86 and 14%, respectively, in agreement with the nucleophilic character of alkyl free radicals and the positive charge of the 2-carbon atom of the thiazole (6). 

Schatzmann, in 1891, tried to prepare 2-thiazolines by hydrogenation of thiazoles and by the action of sodium and ethanol on 2,4-dimethyl-thiazole, 2-methylthiazole, and 2-methyl-4-phenylthiazole (476). None of these substrates was reduced to thiazoline the second gave no reaction and the first underwent ring cleavage, leading to a mixture of n-propylmercaptan and ethylamine (Scheme 90). Three years later the same... 

Note however that Table 4 3 mcludes two entries for propane The second entry corresponds to the cleavage of a bond to one of the hydrogens of the methylene (CH2) group It requires slightly less energy to break a C—H bond m the methylene group than m the methyl group... 

Cleavage of the carbon-carbon bond in ethane yields two methyl radicals whereas propane yields an ethyl radical and one methyl radical Ethyl radical is more stable than methyl and so less energy is required to break the carbon-carbon bond in propane than in ethane The measured carbon-carbon bond dissociation energy in ethane is 368 kJ/mol (88 kcal/mol) and that in propane is 355 kJ/mol (85 kcal/mol)... 

FIGURE 5 2 Interconversion of as and trans 2 butene proceeds by cleavage of the tt component of the double bond The yellow balls represent methyl groups... 

In the acid catalyzed dehydration of 2 methyl 1 propanol what carbocation would be formed if a hydride shift accompanied cleavage of the carbon-oxygen bond in the alkyloxonium lon" What ion would be formed as a result of a methyl shift" Which pathway do you think will predominate a hydnde shift or a methyl shift" ... 

With electrons flowing from ethylene to zirconium the Zr—CH3 bond weakens the carbons of ethylene become positively polarized and the methyl group migrates from zirconium to one of the carbons of ethylene Cleavage of the Zr—CH3 bond is accom panied by formation of a ct bond between zirconium and one of the carbons of ethylene m Step 3 The product of this step is a chain extended form of the active catalyst ready to accept another ethylene ligand and repeat the chain extending steps... 

Unlike Its acid catalyzed counterpart a halogenation m base cannot normally be limited to monohalogenation Methyl ketones for example undergo a novel polyhalo genation and cleavage on treatment with a halogen m aqueous base... 

Only one site for periodic acid cleavage in methyl a D arabmofuranoside... 

Haloform reaction (Section 18 7) The formation of CHX3 (X = Br Cl or I) brought about by cleavage of a methyl ketone on treatment with Br2 CI2 or I2 in aqueous base... 

---