Oxidation reactions migrating group mechanism

Figure 11.7. Reactions of nitric oxide involving sulfhydryl groups, a Hypothetical mechanism of nitrosothiol formation. The superoxide anion generated may reaet with a seeond moleeule of NO to yield peroxynitrite. b Migration of nitroso groups between sulfhydryls. This is experimentally illustrated in Figure 11.9b.

All of these reactions are illustrative of the very powerful nucleophilicity that organocuprates exhibit toward carbon. The reactions are generally considered to proceed by direct displacement on the substrate. Secondary tosylates react with inversion of stereochemistry, as is the case for classical Sn2 reactions. " The overall mechanism probably consists of two steps. First an oxidative addition to the metal in which the copper acts as a nucleophile. This is followed by migration of one of the alkyl groups from copper. This kind of process is well documented by mechanistic studies with other types of organometallic compounds. 

The most widely used reaction of organoboranes is the oxidation to alcohols, and alkaline hydrogen peroxide is the reagent usually employed to effect the oxidation. The mechanism, which is outlined below, involves a series of B to O migrations of the alkyl groups. The R—O—B bonds are hydrolyzed in the alkaline aqueous solution, generating the alcohol. 

In acyclic systems the 1,4-relative stereoselectivity was controlled by the stereochemistry of the diene. Thus, oxidation of (E,E)- and (E,Z)-2,4-hexadienes to their corresponding diacetates affords dl (>88% dl) and mesa (>95% me so) 2,5-diacetoxy-3-hexene, respectively. A mechanism involving a t vans-accto xy pal I adation of the conjugated diene to give an intermediate (rr-allyljpalladium complex, followed by either a cis or trans attack by acetate on the allyl group, has been suggested. The cis attack is explained by a cis migration from a (cr-allyl)palladium intermediate. The diacetoxylation reaction was applied to the preparation of a key intermediate for the synthesis of d/-shikimic acid, 3,... 

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