1522
A. CORRUBLE et al.
high field NMR approach. Amide derived from 3a has been prepared by deprotonating the amine
with Bu6Li (obtained following Fraenkel's procedure 16) in ds-THF at - 7 0 ° C directly in the NMR
tube. One equivalent of a tolualdehyde solution in the same solvent has then been slowly added with
vigorous stirring, under an ultra-dry argon atmosphere while remaining at the same temperature. The
IH NMR spectrum recorded right after did not exhibit any signal for the aldehyde while five singlets
showed up in 6.21-5.85 ppm region. Obtention of these five new signals, for the benzylic proton ~x
to both a nitrogen and an oxygen atoms, possibly stems from the formation of two diastereoisomers
during this condensation and from the coexistence of several aggregated forms in THE On the 13C
NMR, we could not observe any carbonyl-corresponding signal but a new peak at 87.5 ppm which
would fit an hemiaminal-type carbon. Finally, the 6Li signal at 1.89 ppm17 originally observed for
the amide derived from 3a4 was totally replaced by a main singlet at 0.87 ppm, together with smaller
peaks at 0.79 and 0.73 ppm. These chemical shifts compare well to those reported in the literature
for lithium alcoholates (0.75-0.80 ppm).18 This whole set of data seems to constitute a fair body of
evidence in support to the formation of 6 in the case of amide 3a(Li). The procedure12 followed in
Table 1 puts formation of 5 and 6 in competition.
In conclusion, 3-aminopyrrolidines appear to be promising structures for enantioselective transfor-
mations. The synthetic access we propose for both enantiomerically pure forms of these new chiral
auxiliaries is simple (2 steps from commercially available (R) or (S)-3-aminopyrrolidine to 3a-h).
In the butyllithium condensation onto aromatic aldehydes, their lithium amides can afford alcohols
featuring e.e.s as high as 73%, provided the substituent borne by the 3-amino group is bulky enough.
Extensions to this work and further applications for these diamines will be reported in due course.
Acknowledgements
Dr Yann Prigent (Univ. of Rouen) for its expertise with the 500 MHz NMR equipment and the
Minist6re de la Recherche et de la Technologie for a grant to A. C.
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