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20.2.7.1.3.4.1 Method 1: Stereoselective Birch Reduction of Chiral Pyrrole-2-carboxylates

DOI: 10.1055/sos-SD-020-00343

Wolkenberg, S. E.; Garbaccio, R. M.Science of Synthesis, (200720461.

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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