Catalytic Enantioselective α‐Ethynylation of Oxindoles: Total Synthesis of (‐)‐Corynoxine, (‐)‐Isorhynchophylline, (‐)‐Aspidospermidine, and (‐)‐Limaspermidine

The all-carbon quaternary stereogenic center of oxindoles is a crucial structural element of a broad spectrum of indole alkaloids, imparting these molecules with rigid three-dimensional configurations essential for their biological activities. Here, we present a catalytic asymmetric α-ethynylation reaction of oxindoles taking advantage of the catalysis of a spiropyrrolidine amide (SPA) triazolium. This transformation enables the enantioselective construction of the C3 quaternary carbon stereocenter of oxindoles while introducing a versatile ethynyl functionality. Employment of this methodology has been demonstrated in the divergent total synthesis of indole alkaloids (-)-corynoxine, (-)-isorhynchophylline, (-)-aspidospermidine, and (-)-limaspermidine, featuring a protecting group-dependent 1,6-Michael addition or an aminolysis/1,6-Michael addition sequence to generate two distinct types of spiro-indoles, tailored for different late-stage synthetic purposes.