Amines tert. s. below

Rate constants for the hydrogen abstraction from (Me3Si)3SiH by diaryl aminyl radicals 20-24 were determined by using a method in which the corresponding amines catalyse the reaction of 2,4,6-tri-tert-butylphenoxyl radical with (McsSOjSiH (see below). At 91 °C, rate constants are 33.5, 7.27, 5.63, 2.45 and 45.8 s for radicals 20, 21, 22, 23 and 24, respectively [22]. Based... 

The above drawbacks of crystalline photoreactions are circumvented in an approach called the ionic auxiliary approach which is outlined below [185-207]. Scheffer and coworkers make a salt of a substrate having a carboxylic acid with a chiral organic amine or vice versa. The chirality of the amine would necessitate that the salt crystallize in a chiral space group. The crystal formed in this fashion would also be able to withstand higher conversions due to stronger lattice forces in these crystals. An example of this type of approach is shown in Scheme 8. Treatment of the dibenzobarralene derivative 18, with the tert-butyl ester of (S)-proline 19, afforded salt 20 irradiation of the crystals of this salt gave diester 21. In this reaction, only one regioisomer 21 is formed, and this product is formed in over 95% ee. More examples are to be found in Chap. 12. 

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