Sequential protocol for C(sp)-H carboxylation with CO2: KO (t) Bu-catalyzed C(sp)-H silylation and KO (t) Bu-mediated carboxylation

CO2 incorporation into C-H bonds is an important and interesting topic. Herein a sequential protocol for C(sp)-H carboxylation by employing a metal-free C-H activation/catalytic silylation reaction in conjunction with KO (t) Bu-mediated carboxylation with CO2 was established, in which KO (t) Bu catalyzes silylation of terminal alkynes to form alkynylsilanes at low temperature, and simultaneously mediates carboxylation of the alkynesilanes with atmospheric CO2. Importantly, the carboxylation further promotes the silylation, which makes the whole reaction proceed very rapidly. Moreover, this methodology is simple and scalable, which is characterized by short reaction time, wide substrate scope, excellent functional-group tolerance and mild reaction conditions, affording a range of corresponding propiolic acid products in excellent yields in most cases. In addition, it also allows for a convenient C-13-labeling through the use of (CO2)-C-13.