Anti-Markovnikov versus

A Summary of Markovnikov versus Anti-Markovnikov Addition of HBr to Alkenes... 

In hydrocarboxylations, as in the 0x0 process, selectivity of linear versus branched products is an important issue, because (in general) mixtures of isomeric carboxylic acids are obtained, owing not only the occurrence of both Markovni-kov and anti-Markovnikov addition of the alkene to the metal hydride, but also to metal-catalyzed alkene isomerization (eq. (2)). In the case of higher olefins, Co2(CO)g as catalyst leads to a number of different carboxylic acid isomers due to the isomerization activity of the catalyst. 

Reversal of the regioselectivity has been observed for the Wacker-Tsuji oxidation of alkene systems. Mechanistically, the regiochemistry of the Wacker-Tsuji oxidation stems from the Markovnikov addition (which takes place for the vast majority of the cases) versus the anti-Markovnikov regioselectivity although methyl-ketone 2 is often the major product and aldehyde 7 is the minor product. However, abnormal regiochemistry has been observed where aldehyde 7 is the major or even sole product in the Wacker-Tsuji oxidation. 

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