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

Abstract 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.