Lactonization of 2-Alkynylbenzoates for the Assembly of Isochromenones Mediated by BF3·Et2O.

A general and efficient lactonization method of readily available 2-alkynylbenzoates affording biologically important isochromenones has been realized via a solely BF3·Et2O-mediated 6-endo-dig cyclization process under mild conditions. An alternative mechanistic pathway in which BF3·Et2O activates the carbonyl of the ester moiety, rather than the alkyne triple bond, was postulated on the basis of control experiment results. Gram-scale reaction and further application for the assembly of more complex molecules demonstrated the practicability of the protocol.

Synthesis of trifluoromethylated 2H-azirines through Togni reagent-mediated trifluoromethylation followed by PhIO-mediated azirination.

The reaction of enamine compounds with the Togni reagent in the presence of CuI afforded ß-trifluoromethylated enamine intermediates, which were converted directly to biologically interesting trifluoromethylated 2H-azirines by an iodosobenzene (PhIO)-mediated intramolecular azirination in a one-pot process.

Synthesis of Spirooxindoles from N-Arylamide Derivatives via Oxidative C(sp2)-C(sp3) Bond Formation Mediated by PhI(OMe)2 Generated in Situ.

A class of novel spirooxindole compounds (2) were readily synthesized, in a metal-free environment, from N-arylamide derivatives (1) via intramolecular oxidative cyclization. Direct oxidative C(sp2)-C(sp3) bond formation was realized with the least-studied PhI(OMe)2 as an oxidant, formed in situ from the reaction between PhIO and MeOH.

Ultrastructural changes and location of beta-1, 3-glucanase in resistant and susceptible cotton callus cells in response to treatment with toxin of Verticillium dahliae and salicylic acid.

Calli from two cotton cultivars susceptible and resistant to Verticillium wilt, were treated with a crude toxin of Verticillium dahliae (VD-toxin) plus salicylic acid (SA). Cells treated with VD-toxin showed distinct ultrastructural changes. Cells from the susceptible cultivar displayed damage to plasma membrane and cytoplasm. The deleterious effect on cells of the resistant cultivar, with an accumulation of electron-dense precipitate in the vacuoles, was less noticeable. Exogenous SA protected callus cells from VD-toxin. We also report the localization of beta-1,3-glucanase in callus cells with immunofluorescence Labeling. Stronger fluorescence was observed in the extracellular space in resistant than in susceptible cotton; strongest in resistant cotton after 5 days of treatment with VD-toxin plus SA. The findings reported here indicate an important role of exogenous salicylic acid in the induction of resistance to VD-toxin in cotton. Coupled with an increase in beta-1,3-glucanase, cellular integrity is maintained and damage to cell wall and plasma membrane is avoided.