Exciplex diastereomeric

Scheme 2 is the simplest but not the only reaction scheme conceivable. The deactivation of, say, S may proceed via an excimer (SS) or a diastereomeric exciplex (SR). The same deactivation pattern holds, of course, for R, so that the deactivation in toto is nonasymmetric. If there were exciplex emission, circularly polarized fluorescence might be observed. Inoue discusses also a hot ground state path of deactivation [37]. 

From mechanistic studies, it was revealed that the exciplex formation i reversible and the product ee is determined by both the relative stability of diastereomeric exciplexes and the relative rate of subsequent alcohol attad [70b,c]. It should be noted that the introduction of saccharide auxiliaries to... 

Enantiomeric (E)-cyclooctene (20E) was first resolved in 1963 through its diastereomeric platinum(II) complex. Synthesis of optically active 20E has been the subject of intensive study since 1968. The first preparation involves the treatment of enantiopure (E)-cyclooctane-l,2-thiocarbonate with triisooctyl phosphate or of (E)-cyclooatane-l,2-trithiocarbonate with l,3-dibenzyl-2-methyl-l,3,2-diazaphospholi-dine. Following analogous synthetic routes, enantiomeric (E)-cycloheptene (18E) can be produced and trapped by 2,5-diphenyl-3,4-isobenzofuran as an optically active adduct. In 1973, the circular dichroism spectrum of enantiopure 20E vapor was recorded in the vacuum UV region down to 150 nm. The first enantiodifferentiating Z-E photoisomerization of cyclooctene sensitized by chiral benzenecarboxylates appeared in 1978. Transfer of chiral information from sensitizer to substrate occurs within the exciplex intermediate. ... 

In the presence of enantiomerically enriched sensitizer 36 (77% ee), the observed enantiomeric excesses increased from 1% ee at room temperature to 15% ee at -65°C2 With the enantiomerically enriched anthracene derivative 37 (91% ee), the enantioselectivity was enhanced to 23% ee at -65°C, favoring the opposite enantiomer. Based on fluorescence quenching experiments and the concentration dependence of the observed enantioselectivities, the authors suggest the formation of diastereomeric exciplexes by complexation of the different prochiral faces of the styrene to the chiral surface of the sensitizer. The... 

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