Hypervalent organoantimony compounds 12-ethynyl-tetrahydrodibenz[c,f][1,5]azastibocines: Highly efficient new transmetallating agent for organic halides

Extremely efficient and high-speed ethynylation of acyl chlorides, aryl iodides and bromides was demonstrated by palladium-catalyzed cross-coupling reaction of N-t-butyl-Sb-ethynyl-5,6,7,12-tetrahydrodibenz[c,f][1,5]azastibocine under mild conditions. Optimization and generalization of the hypervalent antimony-mediated coupling reaction are presented in detail. Single-crystal X-ray analysis of the N-methyl-1,5-azastibocine revealed that the remarkable reactivity enhancement of the azastibocine was derived from elongation of the antimony–ethynyl carbon bond originated from Sb–N intramolecular non-bonding interaction.