Catalytic Enantioselective Protonation of Nitronates Utilizing an Organocatalyst Chiral Only at Sulfur

The highly enantioselective protonation of nitronates
formed upon
the addition of α-substituted Meldrum’s acids to terminally
unsubstituted nitroalkenes is described. This work represents the
first enantioselective catalytic addition of any type of nucleophile
to this class of nitroalkenes. Moreover, for the successful implementation
of this method, a new type of N-sulfinyl urea catalyst
with chirality residing only at the sulfinyl group was developed,
thereby enabling the incorporation of a diverse range of achiral diamine
motifs. Finally, the Meldrum’s acid addition products were
readily converted to pharmaceutically relevant 3,5-disubstituted pyrrolidinones
in high yield.