Enantioselective Phase‐Transfer Catalyzed α‐Sulfanylation of Isoxazolidin‐5‐ones: An Entry to β 2,2 ‐Amino Acid Derivatives

An unprecedented enantioselective α‐functionalization of C4‐substituted N ‐alkoxycarbonyl isoxazolidin‐5‐ones, readily available platforms from Meldrum's acid derivatives, by N ‐sulfanylphthalimide (PhthSR) electrophiles was achieved upon an efficient phase‐transfer catalytic approach, mediated by a commercial N ‐spiro quaternary ammonium catalyst. Two catalytic activities of the in situ formed R 4 N + Phth − species were highlighted, the phtalimidate being involved in the anion metathesis event and likely as a Brønsted base. This sequence offers a straightforward access to α,α‐disubstituted isoxazolidinones, which turned out to be useful precursors of α‐sulfanyl‐β 2,2 ‐amino acid derivatives.