title: Synthesis, structure, and reaction of 1-alkynyl(aryl)-lambda3-bromanes.
abstract: Reported here for the first time are the synthesis, structure, and reaction of hypervalent 1-alkynyl(aryl)-lambda3-bromanes. BF3-catalyzed ligand exchange on bromine(III) of p-trifluoromethylphenyl(difluoro)-lambda3-bromane with 1-alkynyl(trimethyl)stannanes in dichloromethane at -78 degrees C afforded 1-alkynyl(aryl)-lambda3-bromanes in good yields. Trimethyl(trimethylsilylethynyl)stannane gave silylethynyl-lambda3-bromane selectively. 13C NMR chemical shifts of acetylenic carbon atoms of alkynylbromanes are compared with those of alkynyl-lambda3-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)-lambda3-bromanes serve as highly electron-deficient Michael acceptors and undergo tandem Michael-carbene rearrangements by the reaction with sulfonate anions, yielding 1-alkynyl sulfonates.
authors.affiliation: Faculty of Pharmaceutical Sciences, University of Tokushima, 1-78 Shomachi, Tokushima 770-8505, Japan. mochiai@ph.tokushima-u.ac.jp
authors.forename: Masahito
authors.initials: M
authors.lastname: Ochiai
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Nishi
authors.forename: Satoru
authors.initials: S
authors.lastname: Goto
authors.forename: Motoo
authors.initials: M
authors.lastname: Shiro
authors.forename: Hermann J
authors.initials: HJ
authors.lastname: Frohn