Preparation of Enantiomerically Pure Perfluorobutanesulfinamide and Its Application to the Asymmetric Synthesis of α‑Amino Acids

A high
yielding and practical two-step synthesis of enantiomerically
pure perfluorobutanesulfinamide from Senanayake’s 2-aminoindanol-derived
sulfinyl transfer reagent was developed and carried out on a multigram
scale. Straightforward condensation of this sulfinamide with ethyl
glyoxylate provided the N-perfluorobutanesulfinyl
imino ester. The utility of this activated N-sulfinyl
imino ester was demonstrated for reactions that gave either no product
or very low yields with the corresponding less electrophilic N-tert-butanesulfinyl derivative. Specifically,
the Rh­(III)-catalyzed C–H bond addition of aromatic compounds
to the N-perfluorobutanesulfinyl imino ester provided
arylglycines with very high diastereoselectivities for a range of
directing groups including pyrrolidine amide, azo, sulfoximine, 1-pyrazole,
and 1,2,3-triazole functionalities. Thermal asymmetric aza-Diels–Alder
reactions also proceeded in good yields and with high selectivity,
including for the substituted dienes (E)-1,3-pentadiene
and (2E,4E)-2,4-hexadiene.