Regioselectivity properties

Halide anions affect the rate of hydroformylation of internal olefins as well as the regioselective properties of the catalyst [136]. The rate of hydroformylation of thermally equilibrated internal higher alkenes increased by a factor of 6-7 by adding substoichiometric amounts (with respect to palladium) of Cl" or Br" and by a factor of 3-4 with I" [137]. When a thermally equilibrated mixture of internal Cg-Cj g olefins was subjected to isomerization-hydroformylation, a reverse effect on regioselectivity was observed [136e]. Thus, the formation of the linear aldehyde increased in the following order iodide > bromide > chloride. 

The regioselectivity and syn stereochemistry of hydroboration-oxidation coupled with a knowledge of the chemical properties of alkenes and boranes contribute to our under standing of the reaction mechanism... 

One particular feature of ionic liquids lies in their solvation properties, not only for hydrophobic compounds but also for hydrophilic compounds such as carbohydrates. Park and Kazlauskas reported the regioselective acylation of glucose in 99 % yield and with 93 % selectivity in [MOEMIM][BF4] (MOE = CH3OCH2CH2), values much higher than those obtained in the organic solvents commonly used for this purpose (Entry 18) [22] (Scheme 8.3-4). 

Here, the orbital phase theory sheds new light on the regioselectivities of reactions [29]. This suggests how widely or deeply important the role of the wave property of electrons in molecules is in chemistry. 

Recently, the distribution of 2,3-dihydroxybenzoate decarboxylase has been found in a variety of fungal strains (unpubhshed data), and the carboxylation activity for catechol is confirmed by the reaction using resting cells (or cell-free extract) in the presence of 3M KHCO3. The detailed comparative studies of enzyme structures and catalytic properties between 2,3-dihydroxybenzoate decarboxylase and 3,4-dihyroxybenzoate decarboxylase might explain how the decarboxylases catalyze the regioselective carboxylation of catechol. 

A catalyst used for the u-regioselective hydroformylation of internal olefins has to combine a set of properties, which include high olefin isomerization activity, see reaction b in Scheme 1 outlined for 4-octene. Thus the olefin migratory insertion step into the rhodium hydride bond must be highly reversible, a feature which is undesired in the hydroformylation of 1-alkenes. Additionally, p-hydride elimination should be favoured over migratory insertion of carbon monoxide of the secondary alkyl rhodium, otherwise Ao-aldehydes are formed (reactions a, c). Then, the fast regioselective terminal hydroformylation of the 1-olefin present in a low equilibrium concentration only, will lead to enhanced formation of n-aldehyde (reaction d) as result of a dynamic kinetic control. 

Takano, T. and Nakatsubo, F. (2010) Synthesis and structure/property relationships of regioselective 2-0-, 3-0-and 6-O-ethyl celluloses. Macromolecular Bioscience, 10, 638-647. 

Some proteases show an esterase activity, especially in their catalytic activity for regioselective acylation of sugars. By utilizing this property, enzymatic synthesis of polyester containing sugar group in the backbone was demonstrated... 

Ford and co-workers reported regioselective substitutions of 2,3-dichloro-6-amino-quinoxaline 270 with various dialkylamines to study the biological properties of substituted quinoxalines <00TL3197>. For example, 2,3-dichloro-6-aminoquinoxaline 270 reacted with nucleophiles to give the opposite regioisomer to that seen with 2,3-dichloro-6-nitroquinoxalines 267. 

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