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Wolkenberg, S. E.; Garbaccio, R. M., Science of Synthesis, (2007) 20, 461.
8-Phenylmenthol and trans-2-(α-cumyl)cyclohexanol (TCC) act as effective chiral auxiliaries for the stereoselective Birch reduction of pyrrole-2-carboxylates 242 and lead respectively to either antipode of the dehydroproline amino acid 244.[198] The intermediate anions are quenched with several electrophiles (Scheme 64) and the diastereoselectivities are moderate to high for this high-yielding transformation. Column chromatography of the diastereomeric product 243 further enhances the diastereomeric excess, and removal of the chiral auxiliary is effected via a two-step sequence without stereochemical erosion.
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M8M | ee | Meeee (%) ee 888 | Mee |
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MeM | 8:8 | 88 | [888] |
MeM | 88:8 | 88 | [888] |
eMeM | 88:8 | 88 | [888] |
MeMe | –e | 88 | [888] |
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References
[198] | Meeeeee, M. M.; Meee, M. M.; Meeeeeeee, M., Meeeeeeeeee Meee., (8888) 88, 888. |