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.
Mandal et al. (Sun,) studied this question.