Stability and Reactivity of 1,3-Benzothiaphosphole: Metalation and Diels–Alder Chemistry

The synthesis and functionalization
of the parent 1,3-benzothiaphosphole
is reported. The phosphole could not be isolated, but the compound
could be manipulated in solution to produce several new phosphorus
compounds. Metalation of the 2-position using lithium diisopropylamide
proceeded smoothly according to 31P NMR spectroscopy, and
quenching with trimethylsilyl chloride resulted in the desired 2-(trimethylsilyl)-1,3-benzothiaphosphole.
The PC bond of the thiaphosphole was also explored as a dienophile
in Diels–Alder reactions with isoprene, 2,3-dimethylbutadiene,
2,3-dibenzylbutadiene, and cyclopentadiene. The fused-ring structures
were fully characterized, and a solid-state molecular structure of
the 2,3-dimethylbutadiene cycloadduct was obtained. Residual dipolar
coupling (RDC) NMR experiments were used to assign major and minor
products for the isoprene and cyclopentadiene adducts.