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

Abstract : 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 R4N+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‐β2,2‐amino acid derivatives.