Sequential protocol for C(sp)–H carboxylation with CO₂: KO^tBu-catalyzed C(sp)–H silylation and KO^tBu-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^tBu-mediated carboxylation with CO₂ was established, in which KO^tBu 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 ¹³C-labeling through the use of ¹³CO₂.