Insights into the unexpected chemoselectivity in Brønsted acid catalyzed cyclization of isatins with enaminones: convenient synthesis of pyrrolo[3,4-c]quinolin-1-ones and spirooxindoles.
Divergent cascade syntheses constitute a highly attractive and challenging area in synthetic chemistry, and can exhibit unexpected chemoselectivity. Herein, a Brønsted acid-controlled protocol is described for the efficient catalysis of two different reactions, namely acylation cascade- and [1+2+3]-type cyclization of enaminones and isatins for the concise synthesis of highly functionalized pyrrolo[3,4-c]quinolin-1-ones and spirooxindoles in the presence of carboxylic acids and KHSO4, respectively. The observed chemoselectivity was reasonably explained by trapping the intermediate α,β-unsaturated 2-oxindoles, and the source of the hydroxyl group, carbocation intermediate, and amination reaction were also evaluated.
Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, 650504, P. R. China. yufuchao05@126.com.
Hui
H
Xu
Bei
B
Zhou
Pan
P
Zhou
Jie
J
Zhou
Yuehai
Y
Shen
Fu-Chao
FC
Yu
Ling-Ling
LL
Lu