Annelation of Phosphole-Substituted Fischer Carbene Complexes by Alkynes

The
reaction of 1-phenyl-2-lithio-3,4-dimethylphosphole with W­(CO)6 at −90 °C followed by methyl triflate at room
temperature gives the complex [(phosphol-2-yl)­methoxycarbene]­pentacarbonyltungsten
(1). This complex reacts with sulfur to give the corresponding
complex [methyl (phosphol-2-yl)­thiocarboxylate]­pentacarbonyltungsten
(2), in which tungsten has migrated from the carbene
to phosphorus. The reaction of 3 with alkynes at 90 °C
gives the corresponding phospholene-annelated cyclopentenones 5 without the need for a nickel catalyst. In one case, an
intermediate vinylketene rearranges by an intramolecular Diels–Alder
reaction to give the tricyclic compound 6. All of the
products have been characterized by X-ray crystal structure analysis.