Catalytic Asymmetric [4 + 1] Annulation of Sulfur Ylides with Copper–Allenylidene Intermediates

The first copper-catalyzed
asymmetric decarboxylative [4 + 1] cycloaddition of propargylic carbamates
and sulfur ylides was successfully developed. This strategy led to
a series of chiral indolines with synthetically flexible alkyne groups
in good yields and with high enantio- and diastereoselectivities (up
to 99% yield, 98% ee, and >95:5 dr). A possible mechanism and stereoinduction
mode with copper–allenylidenes were proposed as the possible
dipolar intermediate.