Markownikov’s rule

X can be COO.R or fe N, and the reaction takes place against Markownikov s rule. 

If (a) these compounds are the initial products of the reaction and (b) the first step in the reaction is an electrophilic attack by bromine (either Br+ or Br+—Bi") then these structures are not consistent with the initial attack being at the gold atom since the electrophilic gold(III) so formed would then be required to attack the olefin. This step would be governed by Markownikov s rule and would give 6 and 7 membered ring... 

If the above assumptions are correct, initial attack by positive bromine must occur on the olefin in accord with Markownikov s rule. The bromine is thus placed as required by the structure of the product, at the end of the side chain in both the vinylphenyl and allyl compounds. 

The major problem in this sequence of reactions is the preparation of the necessary precursors. Fortunately, the addition of iodine azide to olefins has provided a convenient route to many of these compounds. In the majority of the olefiris studied, this addition has been found to be regiospecific and, assuming iodine to be the cation, in accordance with Markownikov s rule. Thus, addition of iodine azide to a terminal olefin followed by dehydroiodination leads to the formation of the internal vinyl azide (equation 3). Moreover, the base-... 

The nucleophile attacks the more alkylated carbon atom. The product is therefore formed by addition of the electrophile to the less substituted end of the double bond and by subsequent addition of the nucleophile to all electrophilic addition reactions including those of type, a statement known as Markownikov s rule. 

Since the EOg reactions are of BEP type, they must proceed via the more stable possible intermediate classical carbonium ion. This will clearly be the one with most alkyl ( — /) groups attached to the cationic center. The electrophile must therefore add to the less alkylated carbon atom, thus following Markownikov s rule. 

On the other hand, Cl, Br", and are all extremely electronegative. The corresponding cyclic compounds consequently react with nucleophiles according to Markownikov s rule, i.e., in an anti-S 2 manner. These compounds are best represented as n complexes [see equation (5.219)]. A very nice final touch is provided by oxygen. As we have seen, propylene oxide reacts with nucleophiles in 5 2 manner [e.g., equation (5.220)]. However, acid-catalyzed ring opening leads to Markownikov-type products formed by nucleophilic attack by solvent on protonated epoxide. 

Note that addition of HX by this mechanism gives products violating Markownikov s rule. Thus electrophilic addition of HBr to propene gives isopropyl bromide, CH3CHBrCH3, not n-propyl bromide. The reversal of addition of HBr under conditions where the radical chain mechanism operates is synthetically useful since it allows one to convert terminal olefins into primary alkyl derivatives. 

Allyl esters of saturated acids have been extensively studied because of the potential application as a silane coupling agent. The addition of silicon hydrides to allyl chloroformate, allyl carbonate, allyl formate, and allyl acetate occurs selectively at the C=C bond according to Farmer s (anti-Markownikov) rule, giving the appropriate /3-adducts although propene and acetoxysilane are also formed as by-products ... 

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