Functional group migration

The biochemistry of coenzyme B12 generally revolves around either mutase enzyme activity, involving functional group migration, notably by stereospecific 1,2-shifts (Scheme 2.8), or methylation by methionine synthetase. The general mechanism for the mutase activity is a radical-based one and has been established by EPR spectroscopy to be of the general form shown in Scheme 2.9. 

Recent studies on the formation of diols such as 19 have shown that functional-group migration reactions are possible when very electron-rich aryl groups are used (Scheme 3.5). In the extreme case of 5-methoxythienyllithium, only the rearranged product 26 was isolated [31]. 

Pyrazolo[4,3-d]-p3uimidine 346 was prepared on refluxing diazido 318 in DMF through 1,5-electrocyclization and functional group migration. Subsequent removal of the ester led to 347 (Scheme 132). Photochemical oxidation of C-4 unsubstituted DHPM analogs, formed uracil-5-carboxyl-ate 348 and 349, respectively (91JCS(P1)1342). 

Conditions 2) and 3) are the most difficult to meet. Reactions which proceed rapidly at room temperature in the solution phase are often sterically hindered in the polymer surface layers. Solvents which permeate into the polymer are likely to aid reaction but may, at the same time, give rise to surface reorganisation, e.g., functional group migration into the bulk. 

Conversion of a ketone to thioamide, wifli functional group migration. 

Allylic rearrangement (Section 10 2) Functional group trans formation in which double bond migration has converted one allylic structural unit to another as in... 

A well-known example of non-prototropic tautomerism is that of azolides (acylotropy). The acyl group migrates between the different heteroatoms and the most stable isomer (annular or functional) is obtained after equilibration. In indazoles both isomers are formed, but 2-acyl derivatives readily isomerize to the 1-substituted isomer. The first order kinetics of this isomerization have been studied by NMR spectroscopy (74TL4421). The same publication described an experiment (Scheme 8) that demonstrated the intermolecular character of the process, which has been called a dissociation-recombination process. 

Use of DMF as a solvent for the oxidation of l-o1efins has been reported by Clement and Selwitz. The method requires only a catalytic amount of PdCl2 and gives satisfactory yields under mild conditions. A small amount of olefin migration product is the only noticeable contaminant in the cases reported. The procedure can be applied satisfactorily to various 1-olefins with other functional groups. This useful synthetic method for the preparation of methyl ketones has been applied extensively in the syntheses of natural products such as steroids,macrolides, dihydrojasmone, and muscone. " A comprehensive review article on the palladium-catalyzed oxidation of olefins has... 

With respect to the olefinic substrate, various functional groups are tolerated, e.g. ester, ether, carboxy or cyano groups. Primary and secondary allylic alcohols, e.g. 14, react with concomitant migration of the double bond, to give an enol derivative, which then tautomerizes to the corresponding aldehyde (e.g. 15) or ketone ... 

IR spectrometer with the use of a simple time-resolved technique. 2D IR spectra are especially suited for elucidating various chemical interactions among functional groups. The type of information contained in a dynamic spectrum is determined by the selection of the perturbation (e.g. migration, drawing, aggregation, etc.). 

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