Allylpotassium compounds

Further investigation of allylpotassium complexes have shown that 2-isopropylallyl potassium does not show diastereotopism of the methyl groups at temperatures as low as —155 °C54,59. Therefore, the activation barrier for interconversion is on the order of 4 kcal mol 1 or lower. Both crotyl (19) and prenyl (20) potassium complexes are further examples of the preference for allylpotassium compounds to exist as symmetric it species. The potassium has the appropriate atomic radius to reach both C(i) and C(3). No increase in stabilization is gained upon addition of solvent. Allylcesium behaves in the same manner. In general, the theoretically calculated rotational barriers (Table 9) are higher... 

The formation of C—C bonds by way of allylpotassium compounds has been reviewed. ... 

AUyl phenyl selenides, 338 Allylpotassium compounds, 638 Allyrselenides, 338... 

In the case of allylpotassium, the metal complex exists as a symmetric n structure. No temperature dependence was shown by either 13C NMR for A5[C(i) —C(3)] or by 1H NMR for substitution with deuterium at Cp). Thompson and Ford measured experimentally a variety of allylalkali metal compounds using variable-temperature NMR in THF-dx45. Addends such as TMEDA, hexamethylphosphoric triamide (HMPA), 15-crown-5-ether, [2.1.1]cryptand and n-butyllithium showed either no change in the spectrum or rapid decomposition of the complexing agent. Measurement of the populations of E (17) and Z (18) isomers of 1-isopropylallylpotassium showed the Z isomer to be more stable (Table 11). 

Allylpotassium derivatives exist in two stereoisomeric (endo or exo) forms.239,240 Although the endo isomer is more stable, the equilibration is slow enough to allow the synthesis of stereoisomeric heterosubstituted derivatives [Eqs. (10.42) and (10.43)]. On the other hand, even the E-alkenes after appropriate equilibration can be transformed to Z-boron compounds 10 ... 

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