Carboxamide-Directed Stereospecific Couplings of Chiral Tertiary Alkyl Halides with Terminal Alkynes

Herein, we report the stereospecific Sonogashira coupling
of a
chiral α-bromocarboxamide possessing a tert-alkyl moiety and an alkyne; this reaction produces a chiral tert-alkylated alkyne in a stereoretentive manner. In this
reaction, both the CuBr/bathophen catalyst system and carboxamide
directing group are essential for achieving the high enantiospecificities
of the couplings. Mechanistic studies of this reaction revealed that
the alkynyl copper species is the key intermediate that coordinates
to the carboxamide group of chiral α-bromocarboxamide.