Methyl groups, migration

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... 

When alkoxypyridazine 1-oxides are heated alone or in the presence of p-toluenesulfonic acid the methyl group migrates from the methoxy group to the A-oxide group. In this manner, 4-methoxypyridazine 1-oxide rearranges to l-methoxypyridazin-4(l//)-one, 5-methoxypyridazine 1-oxide to 2-methylpyridazin-5(2//)-one 1-oxide and substituted 3,6-dimethoxypyridazine 1-oxides to l,3-dimethoxypyridazin-6(l//)-ones. 

Step 3 The methyl group migrates from zirconium to one of the carbons of the ethylene ligand. At the sane time, the tt electrons of the ethylene ligand are used to fonn a a bond between the other carbon and zirconium. 

The reaction of 3-amino-1,2,4-triazine 1-oxide 1 with methyl iodide in the presence of sodium bicarbonate leads to the methylation of the amino group to afford 3-methylamino-l,2,4-tiiazine 1-oxide 123. This iV-oxide 123, under neutral conditions in the presence of Mel, undergoes methyl group migration to the N(2) atom of the 1,2,4-triazine ring, yielding 3-imino-2-methyl-1,2,4-triazine 1-oxide 124. The same product 124 was obtained by direct methylation of compound 1 under neutral conditions (84TL1677). 

The methyl group migrates with its pair of electrons, as a methyl anion, CH3 (a methanide ion). 

Hexamethylbenzene reacts with DMDO via three pathways (i) to an arene oxide, which rapidly rearranges to an oxepin tautomer that then is oxidized to a cw-diepoxide and then to a cis, cis,trans-triepoxide (ii) a methyl group migrates in the first epoxide to give a cyclohexadienone, which then reacts to give a frani -diepoxide (iii) C—H insertion to give the benzyl alcohol and then the corresponding benzoic acid. ... 

When the olefinic precursor to 866 was treated briefly with trifluoromethanesulfonic acid in dichloromethane solution, cyclization occurs with installation of the final dodecahedrane framework bond. The predominant product proved to be 557 in which methyl group migration has also taken pla( °l The symmetry of this first dodecahedrane was apparent from its spectral properties and nicely detailed... 

It is believed that the reaction starts with homolytic cleavage of the cobalt-carbon bond (at a cost of perhaps 100 kJ mol-1)8 to yield a Co(ll) atom and a 5 -decxy-adenosyl radical. This radical then abstracts a hydrogen atom (in Eq. 19.35 from the methyl group). Migration of the —GO)SR group takes place, followed by return of the hydrogen atom from 5 -deoxyadenosine to the substrate. This regenerates the 5 -deoxyadenosyl radical, which can recombine with the Co( I) atom to form the coenzyme. 

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