Electrophilic reactions regioselectivity

TTie condensation of fluormated carbonyl compounds is a versatile approach to the stereo- and regioselective construction of specifically tluonnated materials It is possible to use fluormated reactants in vanous oxidation states and to utilize them either as the nucleophilic or electrophilic reaction partners Stereocontrol in those processes using the fluormated carbonyl compounds m a nucleophilic fashion has lagged behind the achievement of higher yields... 

Few other electrophilic reactions are known. The trimethyl-3/f-pyrazoIe 105 is oxidized by Af-bromoacetamide (NBA) to the bromohydrin 168 and cyclized further to the epoxide 169 by base (Scheme 63).165 Peracid oxidation of 53 gives the mono ALoxide 75 regioselectively (Scheme 28).108... 

VI. AMIDOESTERS. STEREOSELECTIVE, REGIOSELECTIVE AND ELECTROPHILIC REACTIONS AT THE a-CARBON... 

Similarly to derivatives phenylhydrazone, 1,4-dilithio oximes also react with an achiral ester to give a heterocyclic isoxazole ring102 (equation 33). When two of the a-carbons on an oxime of a ketone are able to undergo deprotonation, the question of the deprotonation site arises. It was found that the regioselectivity in the electrophilic reaction of 1,4-dilithioketoxime salts is especially high and the electrophile reacts with the carbon syn to the oximic oxygen. Kofron and Yeh proved that this is the case by... 

Fluorinated carbonyl compounds may be employed in condensation reactions to stereo- and regioselectively construct specifically fluorinated materials. The fluorinated reactants may be utilized as either the nucleophilic or electrophilic reaction partners. 

It is interesting to see completely different regiochemistries in nucleophilic and electrophilic reactions to 1,1-difluoroethene as a model. Scheme 1.55 shows a typical electronic effect of the fluorine atom as a substituent. Electrophiles mostly attack the (3-carbon of 1,1-difluoroethene generating a-difluorinated carbocations as intermediates in contrast to regioselective nucleophilic additions on the a-carbon of 1,1-difluoroethene generating (3-fluorocarbanions. 

Peracids can react with alkanes to give hydroxylated products, as shown in equation (66). This may be an electrophilic reaction because the rate increases with increasing acidity of the peracid. Radical side reactions were thought to be inhibited by added l2. CF3CO3H is also an effective oxidant. The reaction of franj-l,2-dimethylcyclohexane with PhC03H is reported to be 97% stereoselective (retention) and 97% regioselective for tertiary hydroxylation. ... 

It is well documented [95] that direct halogenation of arenes, bromination in particular, is one of the most selective electrophilic reactions yielding almost exclusively para-substituted products. Evidently, however, the use of cyclometalated compounds might drastically change the selectivity in favor of ort/io-halogenated compounds, as shown in Eq. (7.43) [76, 96]. This halogenation is also widely applied as a regioselective reaction method, as shown below in Eq. (7.44) [97]. 

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