Rearrangements of double bonds

Diketones and tetraketones derived from aromatic compounds by conversion of two or four SCH groups into keto groups, with any necessary rearrangement of double bonds to a quinonoid structure, are named by adding the suffix -quinone and any necessary affixes. 

FIGURE 8.22 Reaction of a free radical with an unsaturated lipid and the subsequent rearrangement of double bonds and reaction with molecular oxygen. 

Notably, the strongly basic conditions used in the reaction do not lead to rearrangement of double bonds present elsewhere in the molecule. Thus, a 57% yield of 3,6-bis(methylene)-3,4,5,6-tetrahydro-177-cyclopropa[/i]naphthalene (15) was obtained, in which the exocyclic double bonds did not undergo isomerization to give 3,6-dimethyl-l//-cyclopropa[6]naphthalene. ° ... 

Quinones - Compounds having a fuUy conjugated cyclic dione structure, such as that of benzoquinones, derived from aromatic compounds by conversion of an even number of -CH= groups into -C(=0)- groups with any necessary rearrangement of double bonds. [5]... 

Other Condensation Reactions. BF3-MeOH and BF3 OEt2 with ethanol are widely used in the esterification of various kinds of aliphatic, aromatic, and carhoxyhc acids the reaction is mild, and no rearrangement of double bonds occurs. This esterification is used routinely for stable acids prior to GLC analysis. Heterocyclic carboxylic acids, unsaturated organic acids, biphenyl-4,4 -dicarboxylic acid, 4-aminobenzoic acid, and the very sensitive 1,4-dihydrobenzoic acid are esterified directly. 

Rearrangement of double bonds can take place to give radical sites in the 1, 4 and 1, 6 positions as well. 

The activity of the microbial isomerase or isomerases (Fig. 1.1.) is key to the production of CLA. An isomerase is solely responsible for movement of the methylene-interrupted double bonds in hnoleic and linolenic adds to conjugated positions. Subsequent action of a reductase reduces or eliminates double bonds, but serves no function in rearrangement of double bonds to conjugated positions. Thus, it is the study and regulation of the isomerases that is needed to maximize the quantity of specific CLA isomers. 

DOX adds molecular oxygen to produce 8-hydroperoxy derivatives with linoleic, oleic, vaccenic and ricinoleic acids with no rearrangement of double bonds. The 8-hydroperoxy linoleic and oleic acids may undergo enzymic isomerization to their 7,8-hydroxy derivatives in some fungi [6]. Table 3 shows some examples of 8-DOX products from fungi. 

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