Synthesis of Sterically Congested Z‑Selective Secondary β‑Enaminal

Herein,
a sterically induced reactivity switch has been developed
to achieve the allenal reactivity rather than the classical copper-allenylidene
reactivity of cyclic ethynylethylene carbonates (EECs). This copper-catalyzed
protocol furnished synthetically challenging Z-selective
secondary enaminal containing bulky N-aryl groups.
This reaction operates under mild conditions and avoids using hazardous
chemicals compared to the previously reported methodologies. The success
hinges on the easily accessible sterically bulky anilines, which suppress
direct propargylic substitution and promote addition onto the allenal
intermediate. In addition, late-stage functionalization was carried
out to advance the potential application of this methodology. Further
DFT studies provided insight into the origin of Z-selectivity.