Palladium-catalyzed carbene migratory insertion using conjugated ene-yne-ketones as carbene precursors.
Palladium-catalyzed cross-coupling reactions between benzyl, aryl, or allyl bromides and conjugated ene-yne-ketones lead to the formation of 2-alkenyl-substituted furans. This novel coupling reaction involves oxidative addition, alkyne activation-cyclization, palladium carbene migratory insertion, β-hydride elimination, and catalyst regeneration. Palladium (2-furyl)carbene is proposed as the key intermediate, which is supported by DFT calculations. The palladium carbene character of the key intermediate is validated by three aspects, including bond lengths, Wiberg bond order indices, and molecular orbitals, by comparison to those reported for stable palladium carbene species. Computational studies also revealed that the rate-limiting step is ene-yne-ketone cyclization, which leads to the formation of the palladium (2-furyl)carbene, while the subsequent carbene migratory insertion is a facile process with a low energy barrier (<5 kcal/mol).
Beijing National Laboratory of Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of the Ministry of Education, College of Chemistry, Peking University , Beijing 100871, China.
Ying
Y
Xia
Shuanglin
S
Qu
Qing
Q
Xiao
Zhi-Xiang
ZX
Wang
Peiyuan
P
Qu
Li
L
Chen
Zhen
Z
Liu
Leiming
L
Tian
Zhongxing
Z
Huang
Yan
Y
Zhang
Jianbo
J
Wang