Several PC or Partially CC Double Bonds

Compounds with Several PC or Partially CC Double Bonds 

Phosphacarbapolyenes will be dealt with in this section. Here we have compounds that can be deducted from small polyenes by means of substitution of individual CH moieties with phosphorus atoms, creating PC double bonds in conjugation with another PC or CC sequence. The reactivity most impressively demonstrates the amazing affinity for pure carbon systems. 

Finally, the introduction of the sterically pretentious 2,4,6-tri-t-butylphenyl group in le made it possible to protect the PC double bond from further reactions of the diene, which was assumed to be an intermediate in all other cases presented herein (compound 4k). 

Recent investigations showed that 1-phosphabuta-l,3-dienes can be synthesized by HC1 elimination of the corresponding chlorophosphanes a-c [Eq. (33)]. While b is converted completely into the 1-phospha-butadiene at room temperature within a few hours, the HC1 elimination requires a semimolar surplus of DBU and a prolonged reaction time of 2 weeks (85). 

With c, 6 days at 60- 70°C is necessary to complete the reaction. Sulfur reacts with b to form the thiophosphathiirane, metal carbonyls give rjl complexes, and with norbornadiene the Diels-Alder adduct is 

---