A straightforward and efficient approach to structurally diverse and synthetically useful ring-fluorinated 4H-pyrans via a simple base-mediated cascade reaction of readily available trifluoromethylated alkenes with 1,3-dicarbonyl compounds was developed. The key events of this reaction involve two consecutive C-F substitutions under very mild conditions.

A novel NIS-mediated oxidative cyclization of N-(2-trifluoromethyl-3-alkynyl)hydroxylamines is developed, which provides a facile access to 4-trifluoromethyl-5-acylisoxazoles in 33-91% yields. Various types of commonly used electrophilic halogen source such as ICl, I2, NIS, NBS and NCS at different temperatures in various solvents were investigated. It was found that the NIS acts as both an oxidant and an electrophile for the present sequential transformation. The scope, mechanism and application of this NIS-mediated domino reaction for further synthetic transformation were studied.

No abstract

Hydroxylamines: A Facile Access to 4-Trifluoromethyl-5-acylisoxazoles. -The reaction tolerates activated and deactivated aryl substituents as well as higher perfluorated alkyl residues but fails with terminal alkynes and TMS-terminated alkynes. At low temperatures, the related oxime (VII) as key intermediate can be isolated prior to oxidative cyclization. Further synthetic utilization is demonstrated by the transformation of compound (IIb) to pharmaceutically interesting compound (VIII) in 41% overall yield. -(ZHANG, L.; ZENG, Q.; MAO, A.; WU, Z.; LUO, T.; XIAO*, Y.; ZHANG, J.; Org. Biomol. Chem. 12 (2014) 44, 8942-8946, http://dx.