Gooßen
disclosed the rhodium-catalyzed sequential acylation/cyclization
of benzoic acids with aliphatic anhydrides (Scheme 2b).8
Wen reported the rhodium-catalyzed oxidative coupling of
benzoic acids with 2-alkylvinyl acetates to give a mixture of
isocoumarin and 3-alkylidenephthalide (Scheme 2c).9 However,
these protocols suffer from limitations such as narrow substrate scope, high reaction temperature, moderate regioselectivity,
and/or incomplete Z/E selectivity. Herein we disclose
a rhodium-catalyzed oxidative annulation of benzoic acids with
terminal alkynes to afford 3-ylidenephthalides in a completely Z
selective manner (Scheme 2d). It is noteworthy that this is also
the first example of transition-metal-catalyzed oxidative
coupling/annulation of simple benzoic acids with terminal
alkynes via C−H activation.