On the 6-exo atom transfer radical cyclization reactions of 3-butenyl 2-iodoalkanoates.
Bis(tributyltin)-initiated atom transfer cyclization reactions of 3-butenyl iodoalkanoates in the presence of BF3.OEt2 as the catalyst afforded the 6-exo cyclization products as a mixture of 3,4-cis- and trans-substituted tetrahydro-2H-pyran-2-ones in 53-71% yield with the major isomers being the cis ones. Ab initio calculations at the B3LYP/6-31G level on the transition states of the radical cyclization and on the cyclized products revealed that the reactions are kinetically controlled and the transition states for the 6-exo radical cyclization are in boat conformations. Moreover, the cis-oriented transition states are of lower energy than the corresponding trans-oriented ones, which are in excellent agreement with experimental results.
Fang
Xingang
X
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, P. R. China. clig@pub.sioc.ac.cn
Xia
Hairong
H
Yu
Hui
H
Dong
Xicheng
X
Chen
Minbo
M
Wang
Quanrui
Q
Tao
Fenggang
F
Li
Chaozhong
C