Synthesis of Hypervalent Organobromanes and Threi Synthetic Organic Reactions

点击翻译按钮获取中文摘要

(1)Reported here for the first time are the synthesis, structure, and reaction of hypervalent 1-alkynyl(aryl)-λ^3-bromanes. BF_3-catalyzed ligand exchange on bromine(III) of p-trifluoromethylphenyl(difluoro)-λ^3-bromane with 1-alkynyl(trimethyl)stannanes in dichloromethane at -78℃ afforded 1-alkynyl(aryl)-λ^3-bromanes in good yields. Trimethyl(trimethylsilylethynyl)stannane gave silylethynyl-λ^3-bromane selectively. ^<13>C NMR chemical shifts of acetylenic carbon atoms of alkynylbromanes are compared with those of alkynyl-λ^3-iodanes and explained in terms of the spin-orbit-induced heavy atom effects. The structure of tert-butylethynylbromane was established by a single crystal X-ray analysis of its crown ether complex. The 1-alkynyl(aryl)-λ^3-bromanes serve as highly electron deficient Michael acceptors and undergo tandem Michael-carbene rearrangements by the reaction with sulfonate anions yielding 1-alkynyl sulfonates.(2)Reported here for the first time are the synthesis, isolation, and characterization of hypervalent β-haloalkenyl-λ^3-bromanes. Exposure of terminal alkynes to p-trifluoromethylphenyl(difluoro)-λ^3-bromane activated by BF_3-i-Pr_2O resulted in fluoro-λ^3-bromanation of the triple bonds in a Markownikoff fashion yielding (E)-β-fluoroalkenyl-λ^3-bromanes stereoselectively in good yields. 5-Chloro-1-pentynes undergo domino λ^3-bromanation-chlorine shift-fluorination or λ^3-bromanation-chlorine shift-alkyl shift-fluorination reaction depending on the substituents and afford (E)-β-chloroalkenyl-λ^3-bromanes stereoselectively in high yields. The β-chloroalkenyl-λ^3-bromanes contain three kinds of halogen atoms F,Cl, and Br in the molecule.