Halogen/hydrogen exchange

In Volume 13 reactions of aromatic compounds, excluding homolytic processes due to attack of atoms and radicals (treated in a later volume), are covered. The first chapter on electrophilic substitution (nitration, sulphonation, halogenation, hydrogen exchange, etc.) constitutes the bulk of the text, and in the other two chapters nucleophilic substitution and rearrangement reactions are considered. 

Base-catalyzed displacement reactions, such as base-catalyzed halogenation, hydrogen exchange, and condensation reactions, belong to a separate class of reactions. The reactive species, in this case, is the phenolate ion rather than unionized phenol, and the reactive positions are limited to those ortho and para to the hydroxyl group. In a guaiacyl propane unit, no reaction occurs at positions 2 and 6, and displacement at position 5 will generally proceed more rapidly than the displacement of the side chain. 

Acid-catalyzed hydrogen exchange Halogenation Acylation and alkylation Mercuration Diazo coupling Nitrosation... 

Isoxazoles are presently known to undergo hydrogen exchange, nitration, sulfonation, halogenation, chloroalkylation, hydroxymethylation, Vilsmeier-Haack formylation, and mercuration. The Friedel-Crafts reaction on the isoxazole nucleus has not yet been reported. 

Isoxazole, 3-methoxymethyl-5-methyl-oxidation, 6, 27 Isoxazole, methyl-bromination, S, 88 homolytic halogenation, 6, 51-52 potentiometry, 6, 10 Isoxazole, 3-methyl-basicity, 6, 20 halogenation, 6, 24 hydrogen exchange, 6, 21 sulfonation, 6, 24 synthesis, 6, 83 Isoxazole, 4-methyl-synthesis, 6, 83 Isoxazole, 5-methyl-basicity, 6, 20... 

Lewis acids have been found to increase the rate of hydrogen exchange in halogen acids, and thus iodine increases the rate of hydrogen exchange in hy-... 

The rate coefficients obtained with hydrogen iodide show that the effectiveness of halogen acids in catalysing hydrogen exchange is HF > HBr > HI and, as noted above, this was attributed to the difference in dielectric constant of the media. 

Halogen-lithium exchange of iodide 71 and subsequent addition of 2-acetyl-furan (72) to the resultant organolithium intermediate yielded two diastereomeric tertiary alcohols (dr=l l), which were converted to (E)-olefin 73 with complete diastereoselectivity upon brief exposure to catalytic amounts of concentrated aqueous hydrogen chloride (Scheme 11) [18]. Diastereoselective hydroboration/oxidation of 73 gave largely the desired stereoisomer 74 due to... 

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