Markownikow addition

Therefore, the isomerization depends crucially on the hydride character of the hydrogen atom. The hydride hgands of soft complexes such as [HRh(CO)(PPh3)3] preferably undergo anti-Markownikow addition with the following polarization ... 

With harder compounds such as [HCo(CO)4], in which the hydrogen atom has more protic than hydridic character, Markownikow addition is followed by isomerization (Eq. 2-88). 

Thus the harder cobalt carbonyl compounds are more strongly isomerizing than the softer rhodium species. Furthermore, bulky, soft hgands like PPhs also favor anti-Markownikow addition for steric reasons. 

In TfOH medium, vinylpyrazine undergoes anti-Markownikow addition involving superelectrophilic intermediates. Arylation of such an electrophile with benzene gave 2-phenylethylpyrazine in high yield (eq 42). ... 

The rule of Markownikow states that on addition of hydrogen halides to a double bond the hydrogen always goes to the carbon atom carrying already the largest number of hydrogen atoms. 

The hydrosilation of 1-alkynes can give either Z-or E-isomers (see (E) (Z) Isomers) of the linear vinylsilane or the Markownikow product (equation 5). Reaction of 1-hexyne with trichlorosilane under platinum catalysis conditions gives a mixture of 1- and 2-silyl-l-hexene (78 22). From the E-stereochemistry of the 1-silyl isomer, a yyn-addition mechanism can be assumed. 

NMR studies have shown the reactions of the chiral hydrido clusters [(At3-RC)RuCoM(Cp)(CO)8H] (R = Me, Ph M = Mo, W) with the prochiral alkene H2C=C(C02Me)NHC0Me to be diastereoselective. This formal insertion process produces only one enantiomeric pair of the possible four diastereomeric products, in which the terminal CH2 of the intermediate alkene complex becomes a CH3 group via Markownikow-type addition of the coordinated hydride. This preferred product stereochemistry may arise from the mutual approach during olefin coordination of the two most polar units, the MoCp and C02Me groups, on the same side of the molecule. 

Lipophilic quaternary salts show high catalytic activity in reactions promoted by aqueous hydrohalic acids. Under liquid-liquid PTC conditions, a number of reactions have been realized the conversion of alcohols into alkyl halides the cleavage of ethers the addition of hydrohalic acids to alkenes according to Markownikow s... 

It has recently been found that an appropriately prepared complex of tetraethyl-ammonium bromide with hydrogen bromide reacts with alkynes under anhydrous homogeneous conditions to yield bromoalkenes the addition product follows Markownikow s rule... 

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