Diastereoselective synthesis of quinolizidin-4-one and indolizidin-3-one derivatives with a spirocyclic motif via cascade cyclization using a gold(I)/Brønsted acid relay catalysis

Transition metal catalysed cascade C–C and C–O bond forming events of alkynes

“…A combined catalytic system consisting of gold (5 mol% of IPrAuNTf 2 ) and Brønsted acid (10 mol% of CSA) was used by Nemoto et al to induce the intramolecular carboalkoxylation cascade of alkyne-tethered MOM-protected amides 68a with various nucleophiles 68b for the diastereoselective synthesis of cyclic amides 68c (Scheme 68). 93 Further, to show the capability of these cascades for the enantioselective construction of various motifs, they reported the enantioselective access to cyclopenta[b]indoles through a gold-catalysed intramolecular carboalkoxylation approach. This method involved the treatment of indole-tethered propargyl acetates 69a with 5 mol% of (S)-DTBM-Segphos(AuCl) 2 and 10 mol% AgSbF 6 to give corresponding enol ether 69b, which upon acid-catalysed hydrolysis gave cyclopenta[b]indoles 69c in good yield and excellent enantioselectivities (Scheme 69).…”

“…A combined catalytic system consisting of gold (5 mol% of IPrAuNTf 2 ) and Brønsted acid (10 mol% of CSA) was used by Nemoto et al to induce the intramolecular carboalkoxylation cascade of alkyne-tethered MOM-protected amides 68a with various nucleophiles 68b for the diastereoselective synthesis of cyclic amides 68c (Scheme 68). 93…”