New phosphorus-carbon cage compounds by Diels-Alder and homo Diels-Alder reactions of 1,3,5-triphosphabenzenes with alkenes

Ethylene, various monosubstituted alkenes (acrylic acid derivatives, styren e), as well as some selected disubstituted alkenes (maleic acid derivatives , fumaric acid derivatives, norbornene, cyclopentadiene) undergo Diels-Alde r reactions with the 1,3,5-triphosphabenzenes 1 under mild conditions to fu rnish the dihydrotriphosphabarrelenes 9, 11a-c, 13a-e, 15a-d, 17a,b, and 24 . The monoadduct 26 as well as the diadducts 27 and 28 axe isolated followi ng the reaction with norbornadiene. Cyclopropene is the only alkene to unde rgo a Diels-Alder/homo Diels-Alder reaction sequence to afford the hexacycl ic system 20.