title: Insight into 2α-Chloro-2'(2',6')-(Di)Halogenopicropodophyllotoxins Reacting with Carboxylic Acids Mediated by BF3·Et2O.
abstract: Stereospecific nucleophilic substitution at the C-4α position of 2α-chloro-2'(2',6')-(di)halogenopicropodophyllotoxin derivatives with carboxylic acids mediated by BF3·Et2O was described. Interestingly, this stereoselective products were completely controlled by the reaction time. That is, if the reaction time was prolonged to 24.5-31 h, the resulting compounds were all transformed into the unusual C-ring aromatization products. Additionally, it demonstrated that BF3·Et2O and reaction temperature were the important factors for C-ring aromatization, and AlCl3 could be substituted for BF3·Et2O as a lewis acid for C-ring aromatization. Halogenation of E-ring of 2β-chloropodophyllotoxins with NCS or NBS also led to the same C-ring aromatization compounds. Especially compounds 5c, 6g and 7b exhibited insecticidal activity equal to that of toosendanin.
authors.affiliation: Research Institute of Pesticidal Design &Synthesis, College of Sciences, Northwest A&F University, Yangling 712100, Shaanxi Province, P. R. China.
authors.forename: Lingling
authors.initials: L
authors.lastname: Fan
authors.affiliation: Research Institute of Pesticidal Design &Synthesis, College of Sciences, Northwest A&F University, Yangling 712100, Shaanxi Province, P. R. China.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Zhi
authors.affiliation: Research Institute of Pesticidal Design &Synthesis, College of Sciences, Northwest A&F University, Yangling 712100, Shaanxi Province, P. R. China.
authors.forename: Zhiping
authors.initials: Z
authors.lastname: Che
authors.affiliation: Research Institute of Pesticidal Design &Synthesis, College of Sciences, Northwest A&F University, Yangling 712100, Shaanxi Province, P. R. China.|State Key Laboratory of Crop Stress Biology for Arid Areas, Northwest A&F University, Yangling 712100, Shaanxi Province, P. R. China.
authors.forename: Hui
authors.initials: H
authors.lastname: Xu