Stable aliphatic bromonium ylides (RfSO2)2C--Br+C6H4-p-CF3 (Rf = CF3, CF3(CF2)3) have been synthesized and structurally characterized for the first time. X-ray crystallographic analyses indicated a ylide structure with an sp2 hybridization of the ylide carbanions and with little double-bond character for the ylidic bond. The bromonium ylides selectively undergo transfer of the aryl group to nitrogen heterocycles, such as pyridines, yielding N-arylpyridinium salts. This is in a marked contrast to the reaction of the iodonium ylides, which produces pyridinium ylides through transylidations.
Exposure of 1-alkynyl[p-(trifluoromethyl)phenyl](tetrafluoroborato)-lambda(3)-bromanes to sodium benzenesulfinate or sodium trifluoromethanesulfinate in dichloromethane at 0 degree C under argon resulted in tandem Michael-carbene insertion reactions to produce 1-sulfonylcyclopentenes selectively, with concomitant formation of a small amount of rearranged 1-alkynyl sulfones.
Ring closure reactions O 0130Tandem Michael Addition-Carbene Insertion Reaction of 1-Alkynyl(aryl)(tetrafluoroborato)-λ 3 -bromanes: 1-(Phenylsulfonyl)-and 1-(Trifluoromethylsulfonyl)cyclopentene Annulation. -Exposure of bromanes (I), (V), (VIII) and (X) to sulfinates (II) results in tandem Michael-carbene insertion reactions to produce 1-sulfonylcyclopentenes (III), (VI) and (IX), selectively with concomitant formation of a small amount of rearranged 1-alkynyl sulfones (IV), (VII) and (XI). -(OCHIAI*, M.; TADA, N.; NISHI, Y.; MURAI, K.; Chem. Commun. (Cambridge) 2004, 24, 2894-2895; Fac. Pharm. Sci., Univ. Tokushima, Sho, Tokushima 770, Japan; Eng.) -M. Paetzel 18-036
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