title: Generation and reaction of tungsten-containing carbonyl ylides: [3 + 2]-cycloaddition reaction with electron-rich alkenes.
abstract: Novel tungsten-containing carbonyl ylides 7, generated by the reaction of the o-alkynylphenyl carbonyl derivatives 1 with a catalytic amount of W(CO)(5)(thf), reacted with alkenes to give polycyclic compounds 5 through [3 + 2]-cycloaddition reaction followed by intramolecular C-H insertion of the produced nonstabilized carbene complex intermediates 8. In the presence of triethylsilane, these tungsten-containing carbene intermediates 8 were smoothly trapped intermolecularly by triethylsilane to give silicon-containing cycloadducts 17 with regeneration of the W(CO)(5) species. By this procedure, the scope of alkenes employable for this reaction was clarified. The presence of the tungsten-containing carbonyl ylide 7c was confirmed by direct observation of the mixture of o-ethynylphenyl ketone 1c and W(CO)(5)(thf-d(8)). Careful analysis of the intermediate by 2D NMR, along with the observation of the direct coupling with tungsten-183 employing the (13)C-labeled substrate, confirmed the structure of the ylide 7c. Examination using (E)- or (Z)- vinyl ether revealed that the [3 + 2]-cycloaddition reaction proceeded in a concerted manner and that the facial selectivity of the reaction differed considerably depending on the presence or absence of triethylsilane. These results clarified the reversible nature of this [3 + 2]-cycloaddition reaction.
authors.affiliation: Department of Chemistry, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8551, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kusama
authors.forename: Hideaki
authors.initials: H
authors.lastname: Funami
authors.forename: Masahide
authors.initials: M
authors.lastname: Shido
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Hara
authors.forename: Jun
authors.initials: J
authors.lastname: Takaya
authors.forename: Nobuharu
authors.initials: N
authors.lastname: Iwasawa