The
reaction of triethylamine with the [4 + 2] cycloadducts of
phosphole sulfides and 3-bromo-<i>N</i>-phenylmaleimide
provides a convenient access to phosphinidene sulfides [RPS].
These transient species are trapped by 2,3-dimethyl-1,3-butadiene
to give the previously unknown trivalent [4 + 2] cycloadducts. One
of these (R = Ph) has been characterized as its P-W(CO)<sub>5</sub> complex by X-ray crystal structure analysis. With cyclopentadiene,
the subsequent insertion of a second molecule of [RPS] leads
to a new type of bicyclic product containing a thiadiphospholane
ring
