Unexpected four- and eight-membered organo P-Se heterocycles.

Reaction of [PhP(Se)(micro-Se)](2) (Woollins' reagent, WR) with symmetrically disubstituted diynes: five-membered P(Se)Se(2)C(2) heterocycles and bis-heterocycles with two five-membered P(Se)Se(2)C(2) rings connected through a C-C single bond; (t)Bu-C[triple bond, length as m-dash]C-C[triple bond, length as m-dash]C-(t)Bu reacts differently to afford an unprecedented four-membered P(Se)SeC(2) heterocycle with one unreacted triple bond and a fused bis-heterocycle containing two five-membered P(Se)SeC(3) rings fused at the middle two carbons of the diyne to give a heterocyclic analogue of pentalene, [3.3.0]octa-1-6-diene.