Evaluation of ee by chiral GC and by 1H NMR with the
chiral shift reagent Eu(hfc)3.
Mircea D. Gheorghiu
A. Chiral GC.
A cycloaddition of cyclopentadiene to methacrolein, in principle, yields four
norbornene adducts: two diastereoisomers, namely exo-CHO-3 and endo-CHO-3, and
two enantiomers, R and S for each diastereomer..
An achiral cycloaddition (no catalyst or an achiral Lewis acid) yields more exo
diastereoisomer than endo (see the Table at the bottom of Fig. 1). Each diastereoisomer
is a racemic mixture (50% R+50% S).
A chiral catalyzed cycloaddition preserves and enhances substantially the amount
of the exo norbornene derivative, but also favors one enantiomer over the other.
BLn* (L-Tartaric acid)
CH2Cl2 -78 C
94 : 6
BLn* (D-Tartaric acid)
CH2Cl2 -78 C
92 : 8
Fig. 1. Cycloaddition of cyclopentadiene to methacrolein under uncatalyzed and
chiral catalyzed conditions.
The chiral (Supelco ALPHADEX1202; oven temperature isotherm of 65 �C) GC
traces for a crude sample resulted from the uncatalyzed (Fig.2) and Lewis acid chiral
2 Cyclodextrin (CD) is a chiral component in the stationary phase of a DEX capillary column. Cyclodextrins
are cyclic oligomers of six or more molecules of D(+)-glucose linked through a (1-4) glycosidic bonds. In
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